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/lsp/sync.lua

@@ -53,7 +53,7 @@ local str_utf_end = vim.str_utf_end
 ---@param line string the line to index into
 ---@param byte integer the byte idx
 ---@param offset_encoding string utf-8|utf-16|utf-32|nil (default: utf-8)
---@returns integer the utf idx for the given encoding
+---@return integer utf_idx for the given encoding
 local function byte_to_utf(line, byte, offset_encoding)
   -- convert to 0 based indexing for str_utfindex
   byte = byte - 1
@@ -204,7 +204,7 @@ end
 --- Normalized to the next codepoint.
 --- prev_end_range is the text range sent to the server representing the changed region.
 --- curr_end_range is the text that should be collected and sent to the server.
---
+---
 ---@param prev_lines string[] list of lines
 ---@param curr_lines string[] list of lines
 ---@param start_range vim.lsp.sync.Range