[Screen share] UX tweaks to the screen share & cast permission dialogs.

1) Move the "Cancel" button to the end side.
2) Make the text be start-aligned.

Fixes: 360291114
Flag: NONE small UX changes

Test: Verify share-to-app permission dialog in LTR and RTL, both entire
screen and single app options
Test: Ditto for cast permission dialog
Test: Ditto for system screen record permission dialog
Test: Verify other SysUI dialogs are unchanged
Test: Screenshot tests
Change-Id: I7aadf23026eb499eefc26cd90393258f135fd1db

Change-Id: I7e13b5d48d324547500043c27cc40409fa8d5ab6