feat(docs): generate builtin.txt (#24493)

- eval.lua is now the source of truth.

- Formatting is much more consistent.

- Fixed Lua type generation for polymorphic functions (get(), etc).

- Removed "Overview" section from builtin.txt
  - Can generate this if we really want it.

- Moved functions from sign.txt and testing.txt into builtin.txt.

- Removed the *timer* *timers* tags since libuv timers via vim.uv should be preferred.

- Removed the temp-file-name tag from tempname()

- Moved lueval() from lua.txt to builtin.txt.

* Fix indent

* fixup!

* fixup! fixup!

* fixup! better tag formatting

* fixup: revert changes no longer needed

* fixup! CI

---------

Co-authored-by: zeertzjq <zeertzjq@outlook.com>

.github/workflows/api-docs.yml

@@ -29,7 +29,6 @@ jobs:
         id: docs
         run: |
           python3 scripts/gen_vimdoc.py
-          ./scripts/gen_vimfn_types.lua
           printf 'UPDATED_DOCS=%s\n' $([ -z "$(git diff)" ]; echo $?) >> $GITHUB_OUTPUT
 
       - name: FAIL, PR has not committed doc changes