🍒 kcms/tablet: Parent the action dialog to the overlay instead of the KCM

If we do not, then it always tries to center itself in the page. Whilst this is kind of fine, if your tablet has a bazillion buttons like mine it makes the dialog almost unusable due to it's placement while scrolling.

(cherry picked from commit 9ded3f70)

Co-authored-by: Joshua Goins josh@redstrate.com