Currently pressing tab inserts a tab character. To enable keyboard navigation it should however focus the next item in the focus chain (the send button). Given that this is a simple reply to a text message and not a fully fledged text editor there's probably no need to insert a tab character anyway
CCBUG: 441742
Use a designer file for it
Make sure the focus is on the reply widget
Disable focus from the original text
raise() the dialog when we show it to make sure it's over the other windows