compose: Focus message input on quote-and-reply

Note that we have logic in `handleMessageFocus` to respond to focus
on the message input by auto-focusing the *topic* input in some
cases. That would be annoying if it happened here: you do a
quote-and-reply, and suddenly the topic input is focused?(!)

But that topic auto-focusing should be defeated in all cases where
it was active. In particular, since the previous commit, the topic
input won't be empty; the logic in `handleMessageFocus` will see
that and skip the auto-focus.

Fixes: #5718

src/compose/ComposeBox.js

@@ -448,6 +448,7 @@ const ComposeBox: React$AbstractComponent<Props, ImperativeHandle> = forwardRef(
           _,
         });
         setMessageInputValue(state => state.value.replace(quotingPlaceholder, quoteAndReplyText));
+        messageInputRef.current?.focus();
       } finally {
         setActiveQuoteAndRepliesCount(v => v - 1);
         activeInvocations.current = activeInvocations.current.filter(x => x !== serialNumber);
@@ -464,6 +465,7 @@ const ComposeBox: React$AbstractComponent<Props, ImperativeHandle> = forwardRef(
       topicSelectionAllowed,
       topicInputState.value,
       setTopicInputValue,
+      messageInputRef,
     ],
   );
   useImperativeHandle(ref, () => ({ doQuoteAndReply }), [doQuoteAndReply]);