fix(build): vimdoc tags are not validated #32801

Problem:
"make lintdoc" is not validating vimdoc (:help) tags.

Solution:
- Call `lang_tree:parse()` to init the parser.
- Load netrw 🤢 explicitly, since it was moved to `pack/dist/opt/`.
- Fix invalid help tags.

runtime/doc/develop.txt

@@ -376,10 +376,10 @@ Where possible, these patterns apply to _both_ Lua and the API:
   - See |vim.lsp.inlay_hint.enable()| and |vim.lsp.inlay_hint.is_enabled()|
     for a reference implementation of these "best practices".
   - NOTE: open questions: https://github.com/neovim/neovim/issues/28603
-- Transformation functions should also have a filter functionality when
-  appropriate. That is, when the function returns a nil value it "filters" its
-  input, otherwise the transformed value is used.
-  - Example: |vim.diagnostic.config.format()|
+- Transformation functions should also have "filter" functionality (when
+  appropriate): when the function returns a nil value it excludes (filters
+  out) its input, else the transformed value is used.
+  - Example: See the format() field of |vim.diagnostic.Opts.Float|.
 
 API DESIGN GUIDELINES                                   *dev-api*