Set the elevation on the Compose implementation of QS footer actions

This CL sets the elevation of the Compose implementation of the QS
footer actions to be the same as the View implementation. Without this,
the footer actions will be displayed below the ScrollView used to
display the QS page instead of above, which means that clicks on the
buttons are passed to the ScrollView (when it is scrollable) instead of
the buttons. See b/299104543#comment12 for details and videos.

Bug: 299104543
Test: Ran SettingsButtonTest, PowerMenuButtonTest and AddGuest on
 cf_x86_64_phone-trunk_staging-userdebug
Change-Id: Ib6c66ade87bb473fae6a3b93a2cbc58f5540ecb6