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>

scripts/gen_vimdoc.py

@@ -1359,4 +1359,7 @@ if __name__ == "__main__":
     else:
         main(Doxyfile, args)
 
+    print('Running ./scripts/gen_eval_files.lua')
+    subprocess.call(['./scripts/gen_eval_files.lua'])
+
 # vim: set ft=python ts=4 sw=4 tw=79 et :