lockscreen: sync password across different screens

lockscreen: sync password across different screens

Test plan:

• lock screen in multiscreen setup
• type on one password box, verify password is synced to other screen
• make deletions and insertions in other screen, and verify changes are synced back

CCBUG: 433563

lockscreen: only show UI on screen with mouse

Otherwise one appears on every screen, which is awkward. However, forcing it to be on a particular screen is undesirable, since if that screen is turned off but not unplugged, it may still be sending a signal to the OS and show up as a valid screen to show things on.

To alleviate that concern, always show the UI on the screen with pointer.

Test plan:

• use multiscreen setup and lock screen
• move mouse across screens, verify that only screen with pointer shows controls
• type some password without pressing enter, and repeat previous point

BUG: 409226 CCBUG: 465566

Depends on kscreenlocker!251 (merged) (so marked as draft)