feat(docs): replace lua2dox.lua

Problem:

The documentation flow (`gen_vimdoc.py`) has several issues:
- it's not very versatile
- depends on doxygen
- doesn't work well with Lua code as it requires an awkward filter script to convert it into pseudo-C.
- The intermediate XML files and filters makes it too much like a rube goldberg machine.

Solution:

Re-implement the flow using Lua, LPEG and treesitter.

- `gen_vimdoc.py` is now replaced with `gen_vimdoc.lua` and replicates a portion of the logic.
- `lua2dox.lua` is gone!
- No more XML files.
- Doxygen is now longer used and instead we now use:
  - LPEG for comment parsing (see `scripts/luacats_grammar.lua` and `scripts/cdoc_grammar.lua`).
  - LPEG for C parsing (see `scripts/cdoc_parser.lua`)
  - Lua patterns for Lua parsing (see `scripts/luacats_parser.lua`).
  - Treesitter for Markdown parsing (see `scripts/text_utils.lua`).
- The generated `runtime/doc/*.mpack` files have been removed.
   - `scripts/gen_eval_files.lua` now instead uses `scripts/cdoc_parser.lua` directly.
- Text wrapping is implemented in `scripts/text_utils.lua` and appears to produce more consistent results (the main contributer to the diff of this change).

runtime/lua/vim/treesitter/query.lua

@@ -231,7 +231,7 @@ end
 ---@param lang string Language to use for the query
 ---@param query_name string Name of the query (e.g. "highlights")
 ---
----@return vim.treesitter.Query|nil -- Parsed query. `nil` if no query files are found.
+---@return vim.treesitter.Query|nil : Parsed query. `nil` if no query files are found.
 M.get = vim.func._memoize('concat-2', function(lang, query_name)
   if explicit_queries[lang][query_name] then
     return explicit_queries[lang][query_name]
@@ -1019,6 +1019,8 @@ end
 --- vim.bo.omnifunc = 'v:lua.vim.treesitter.query.omnifunc'
 --- ```
 ---
+--- @param findstart 0|1
+--- @param base string
 function M.omnifunc(findstart, base)
   return vim.treesitter._query_linter.omnifunc(findstart, base)
 end