feat: use unread-command-events when cancelling inline completion

When the inline completion handles `[t]`, we want it to tear down the
completion UI and act as if nothing had happened.

That works fine for single key events (escape, a-z (self-insert-command),
etc.).

Trying to use multi-key commands, on the other hand fails: If `C-x w q` is
bound (e.g. `quit-restore-window`), starting the key combination when inline
completion is active would result in cancel-with-input function being called
only with `C-x` as last-key. If we lookup C-x , it's not bound to a command,
so we do not execute anything. The user then proceeds to type `w q` and ends
up inserting the text "wq" instead of quitting the window.

This fixes that by using the unread-command-events -- that basically leaves
some input to be handled by the next iteration of the event loop.

As a result, we can now successfully call complex key combinations when the
inline completion is active.

lsp-inline-completion.el

@@ -312,6 +312,7 @@ The functions receive the inserted text and the range that was updated by the co
 (defun lsp-inline-completion-cancel ()
   "Close the suggestion overlay."
   (interactive)
+  (message nil) ;; clear echo
   (let ((was-active (lsp-inline-completion--active-p)))
     (lsp-inline-completion--clear-overlay)
 
@@ -326,11 +327,7 @@ The functions receive the inserted text and the range that was updated by the co
 
   (lsp-inline-completion-cancel)
 
-  (let ((command (lookup-key (current-active-maps) (vector event)))
-        (current-prefix-arg arg))
-
-    (when (commandp command)
-      (call-interactively command))))
+  (setq unread-command-events (nconc unread-command-events (list event))))
 
 (defun lsp-inline-completion-next ()
   "Display the next inline completion."