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/uri.lua

@@ -1,4 +1,4 @@
----TODO: This is implemented only for files currently.
+-- TODO: This is implemented only for files currently.
 -- https://tools.ietf.org/html/rfc3986
 -- https://tools.ietf.org/html/rfc2732
 -- https://tools.ietf.org/html/rfc2396
@@ -116,7 +116,6 @@ end
 
 ---Gets the buffer for a uri.
 ---Creates a new unloaded buffer if no buffer for the uri already exists.
---
 ---@param uri string
 ---@return integer bufnr
 function M.uri_to_bufnr(uri)