feat(lsp): support textDocument/onTypeFormatting (#34637)

Implements [on-type
formatting](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.18/specification/#textDocument_onTypeFormatting)
using a `vim.on_key()` approach to listen to typed keys. It will listen
to keys on the *left hand side* of mappings. The `on_key` callback is
cleared when detaching the last on-type formatting client. This feature
is disabled by default.

Co-authored-by: Maria José Solano <majosolano99@gmail.com>

runtime/lua/vim/lsp/protocol.lua

@@ -572,6 +572,9 @@ function protocol.make_client_capabilities()
       linkedEditingRange = {
         dynamicRegistration = false,
       },
+      onTypeFormatting = {
+        dynamicRegistration = false,
+      },
     },
     workspace = {
       symbol = {