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

runtime/lua/vim/lsp.lua

@@ -17,7 +17,6 @@ local if_nil = vim.F.if_nil
 
 local lsp = {
   protocol = protocol,
-  _inlay_hint = require('vim.lsp._inlay_hint'),
 
   handlers = default_handlers,