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/diagnostic.lua

@@ -1,5 +1,3 @@
----@brief lsp-diagnostic
-
 local protocol = require('vim.lsp.protocol')
 local ms = protocol.Methods
 
@@ -287,6 +285,7 @@ end
 --- )
 --- ```
 ---
+---@param _ lsp.ResponseError?
 ---@param result lsp.PublishDiagnosticsParams
 ---@param ctx lsp.HandlerContext
 ---@param config? vim.diagnostic.Opts Configuration table (see |vim.diagnostic.config()|).
@@ -319,6 +318,7 @@ end
 --- )
 --- ```
 ---
+---@param _ lsp.ResponseError?
 ---@param result lsp.DocumentDiagnosticReport
 ---@param ctx lsp.HandlerContext
 ---@param config table Configuration table (see |vim.diagnostic.config()|).