feat(lsp): inlay hints #23984

Add automatic refresh and a public interface on top of #23736

 * add on_reload, on_detach handlers in `enable()` buf_attach, and
  LspDetach autocommand in case of manual detach
* unify `__buffers` and `hint_cache_by_buf`
* use callback bufnr in `on_lines` callback, bufstate: remove __index override
* move user-facing functions into vim.lsp.buf, unify enable/disable/toggle

Closes #18086

scripts/gen_vimdoc.py

@@ -223,7 +223,6 @@ CONFIG = {
             'log.lua',
             'rpc.lua',
             'protocol.lua',
-            'inlay_hint.lua'
         ],
         'files': [
             'runtime/lua/vim/lsp',