feat: support line comments as doc comments

[ilbertt]

Overview
Adds support for line comments (// ...) as doc comments in these places:

• above services:

  // This is a valid doc comment for the service
  service : {
    greet : (text) -> (text);
  }
  

• above actor methods:

  service : {
    // This is a valid doc comment for greet
    greet : (text) -> (text);
  }
  

• above type declarations:

  // This is a valid doc comment for type A
  type A = record {
    my_field : text;
  };
  

• above record and variant fields:

  type A = record {
    // This is a valid doc comment for my_field
    my_field : text;
  };
  
  type B = record {
    // This is a valid doc comment for nat element
    nat;
    text;
  }
  
  type C = variant {
    // This is a valid doc comment for my_variant_field
    my_variant_field : nat;
  };
  

Closes #631.
Closes #621.
Closes #620.
Closes #619.

Considerations
This doesn't break anything, as comments are invisible to the parser.

[github-actions]

Name	Max Mem (Kb)	Encode	Decode
blob	4_224	4_206_559	2_121_065
btreemap	75_456	4_261_360_630	15_241_691_028
nns	192 ($\textcolor{red}{50.00\%}$)	1_966_599 ($\textcolor{green}{-0.01\%}$)	5_474_107 ($\textcolor{red}{0.09\%}$)
nns_list_proposal	1_088	6_814_402 ($\textcolor{red}{0.00\%}$)	67_872_454 ($\textcolor{green}{-0.00\%}$)
option_list	128	7_475_104	25_776_931
text	6_336	4_203_506	7_877_229
variant_list	128	7_531_305 ($\textcolor{red}{0.00\%}$)	24_342_804 ($\textcolor{red}{0.35\%}$)
vec_int16	16_704	123_693_002	1_069_570_587

• Parser cost: 15_211_320 ($\textcolor{red}{1.40\%}$)
• Extra args: 3_146_843

Click to see raw report

---------------------------------------------------

Benchmark: blob
  total:
    instructions: 6.33 M (no change)
    heap_increase: 66 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    calls: 1 (no change)
    instructions: 4.21 M (no change)
    heap_increase: 66 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    calls: 1 (no change)
    instructions: 2.12 M (no change)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: text
  total:
    instructions: 12.08 M (no change)
    heap_increase: 99 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    calls: 1 (no change)
    instructions: 4.20 M (no change)
    heap_increase: 66 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    calls: 1 (no change)
    instructions: 7.88 M (no change)
    heap_increase: 33 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: vec_int16
  total:
    instructions: 1.19 B (no change)
    heap_increase: 261 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    calls: 1 (no change)
    instructions: 123.69 M (no change)
    heap_increase: 261 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    calls: 1 (no change)
    instructions: 1.07 B (no change)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: btreemap
  total:
    instructions: 19.50 B (no change)
    heap_increase: 1179 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    calls: 1 (no change)
    instructions: 4.26 B (no change)
    heap_increase: 159 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    calls: 1 (no change)
    instructions: 15.24 B (no change)
    heap_increase: 1020 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: option_list
  total:
    instructions: 33.25 M (no change)
    heap_increase: 2 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    calls: 1 (no change)
    instructions: 7.48 M (no change)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    calls: 1 (no change)
    instructions: 25.78 M (no change)
    heap_increase: 2 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: variant_list
  total:
    instructions: 31.88 M (0.27%) (change within noise threshold)
    heap_increase: 2 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    calls: 1 (no change)
    instructions: 7.53 M (0.00%) (change within noise threshold)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    calls: 1 (no change)
    instructions: 24.34 M (0.35%) (change within noise threshold)
    heap_increase: 2 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: nns
  total:
    instructions: 23.49 M (0.92%) (change within noise threshold)
    heap_increase: 3 pages (regressed by 50.00%)
    stable_memory_increase: 0 pages (no change)

  0. Parsing (scope):
    calls: 1 (no change)
    instructions: 15.21 M (1.40%) (change within noise threshold)
    heap_increase: 3 pages (regressed by 50.00%)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    calls: 1 (no change)
    instructions: 1.97 M (-0.01%) (change within noise threshold)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    calls: 1 (no change)
    instructions: 5.47 M (0.09%) (change within noise threshold)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: nns_list_proposal
  total:
    instructions: 74.69 M (0.00%) (change within noise threshold)
    heap_increase: 17 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    calls: 1 (no change)
    instructions: 6.81 M (0.00%) (change within noise threshold)
    heap_increase: 3 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    calls: 1 (no change)
    instructions: 67.87 M (-0.00%) (change within noise threshold)
    heap_increase: 14 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: extra_args
  total:
    instructions: 3.15 M (no change)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Summary:
  instructions:
    status:   No significant changes 👍
    counts:   [total 9 | regressed 0 | improved 0 | new 0 | unchanged 9]
    change:   [max +214.65K | p75 +124 | median 0 | p25 0 | min 0]
    change %: [max +0.92% | p75 0.00% | median 0.00% | p25 0.00% | min 0.00%]

  heap_increase:
    status:   Regressions detected 🔴
    counts:   [total 9 | regressed 1 | improved 0 | new 0 | unchanged 8]
    change:   [max +1 | p75 0 | median 0 | p25 0 | min 0]
    change %: [max +50.00% | p75 0.00% | median 0.00% | p25 0.00% | min 0.00%]

  stable_memory_increase:
    status:   No significant changes 👍
    counts:   [total 9 | regressed 0 | improved 0 | new 0 | unchanged 9]
    change:   [max 0 | p75 0 | median 0 | p25 0 | min 0]
    change %: [max 0.00% | p75 0.00% | median 0.00% | p25 0.00% | min 0.00%]

---------------------------------------------------

Only significant changes:
| status | name            | calls |    ins |  ins Δ% | HI |   HI Δ% | SMI |  SMI Δ% |
|--------|-----------------|-------|--------|---------|----|---------|-----|---------|
|   +    | nns::0. Parsing |     1 | 15.21M |  +1.40% |  3 | +50.00% |   0 |   0.00% |
|   +    | nns             |       | 23.49M |  +0.92% |  3 | +50.00% |   0 |   0.00% |

ins = instructions, HI = heap_increase, SMI = stable_memory_increase, Δ% = percent change

---------------------------------------------------
Successfully persisted results to canbench_results.yml

[christoph-dfinity]

Looks good, just some minor nits!

[christoph-dfinity]

Nice!