fix(lsp): make LspNotify more robust #40332

Problem: LspNotify never passed a buffer when executing the autocmds, so
buffer-local LspNotify autocmd subscriptions didn't have the correct buf
in the event metadata. It was also wrapped in a schedule() so the actual
autocmd was delayed until after the event loop.

This could result in the wrong buffer receiving the notification if
multiple LspNotify autocmds with buffer filters were added. Only the
"latest" one would actually receive non-buffer-filtered autocmds, not
the matching one. It also caused listeners to receive the notification
"out of sync" with when the notification is actually sent. If a buffer
is being deleted (which fires a textDocument/didClose notification), the
notification is scheduled and fired after the buffer is already gone.

Solution: For LSP notifications that pertain to a particular buffer, set
it when executing the LspNotify autocmds so the callback functions that
are filtered on that buffer will get the correct notifications and the
metadata buf field will be correct. Additionally, there is no need to
wrap the LspNotify callback in vim.schedule when it can be called inline
when the notification to the rpc server is fired.

This is tested by removing now-unnecessary autocmds from semantic tokens
(InsertEnter and BufWinEnter should no longer be necessary now that
requests are fired by LspNotify). Without this fix, simply modifying a
buffer doesn't actually trigger LspNotify correctly, and the test for
that fails.

test/functional/plugin/lsp/semantic_tokens_spec.lua

@@ -311,6 +311,7 @@ describe('semantic token highlighting', function()
       exec_lua(function()
         _G.server_full = _G._create_server({
           capabilities = {
+            textDocumentSync = vim.lsp.protocol.TextDocumentSyncKind.Full,
             semanticTokensProvider = {
               full = { delta = false },
               range = true,