dialer: Make the dialer focusable but not its buttons

This helps the dialer to behave as a single unit and not a collection of
buttons and simplify the handling of presses on the Return button, avoid
a conflict between the currently selected button and the Submit button.
2 jobs for press-button in 4 minutes and 21 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #2955
librem5
build-debian

00:02:06

24.9%
passed #2956
librem5
build-debian-package

00:02:14