lsp: add $/progress report (#13294)

Heavily inspired by https://github.com/nvim-lua/lsp-status.nvim.
listen to the LspProgressUpdate event to update your statusline.

runtime/lua/vim/lsp.lua

@@ -569,6 +569,8 @@ function lsp.start_client(config)
     -- TODO(remove-callbacks)
     callbacks = handlers;
     handlers = handlers;
+    -- for $/progress report
+    messages = { name = name, messages = {}, progress = {}, status = {} }
   }
 
   -- Store the uninitialized_clients for cleanup in case we exit before initialize finishes.