feat(ALL): check children treesitter languages after parents

[TheLeoP]

• I have read CONTRIBUTING.md
• I have read CODE_OF_CONDUCT.md

This PR is only a proof of concept of what a fix for #2397 would look like.

Thoughts:

• The easiest way to test this could be to create queries for injecting Lua into some Lua strings
• mini.surround doesn't seem to need this change since the cursor always needs to already be on top of the region with a treesitter injection. So, it will be parsed even before this PR when going up the tree.

[echasnovski]

Thanks for the PR!

• The easiest way to test this could be to create queries for injecting Lua into some Lua strings

There are already tests for injected languages (this one for 'mini.ai'). They use built-in Lua -> Vimscript injections.

I think tests for this could use even Lua -> Vimscript -> Lua injections. Like here:

vim.cmd([[
  set cursorline
  lua local a = 1
]])

• mini.surround doesn't seem to need this change since the cursor always needs to already be on top of the region with a treesitter injection. So, it will be parsed even before this PR when going up the tree.

There is less overall complexity if tree-sitter related (and even some other) code in 'mini.ai' and 'mini.surround' is kept as aligned as possible.

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As per this PR, please reduce code duplication. Both parents and children are meant to be processed exactly the same, right? In both 'mini.ai' and 'mini.surround' this processing is rather complicated, so even with two times duplication it adds a lot.