add writable ShadowCandidate ( text, comment, preedit)

[shewer]

wscand = WShadowCandidate(cand, type) --  WShadow(cand, type [,text [, comment[,  inherit_comment]]])
wscand:get_dynamic_type()  --> "WShadow"
wscand.text= "test"

wscand.comment = "test_comment"
wscand.preedit = "test_preedit" 

[0][./lua/selector.lua:43] → scand = ShadowCandidate(ctx:get_selected_candidate(), "tt")
7LuaTypeISt10shared_ptrIN4rime9CandidateEEE: 0x614fb89656d8
[0][./lua/selector.lua:43] → scand.text=33
"明"
[0][./lua/selector.lua:43] → scand.text=44
"明"
[0][./lua/selector.lua:43] → scand.comment
""
[0][./lua/selector.lua:43] → scand.comment=333
""
[0][./lua/selector.lua:43] → scand.preedit
"ab     （日月）"
[0][./lua/selector.lua:43] → scand.preedit=333333
"ab     （日月）"
[0][./lua/selector.lua:43] → wscand = WShadowCandidate(ctx:get_selected_candidate(), "tt")
7LuaTypeISt10shared_ptrIN4rime9CandidateEEE: 0x614fb8be37f8
[0][./lua/selector.lua:43] → wscand.text=3
"3"
[0][./lua/selector.lua:43] → wscand.comment=33
"33"
[0][./lua/selector.lua:43] → wscand.preedit=333
"333"

[hchunhui]

让 ShadowCandidate 可写，有可能直接进到 librime 中吗？