Only force wallpaper visibility events for wearOS

This puts the ag/21736290 logic under a isWearOs flag.

Visibility events should only be sent when there are actual visibility
changes, except for this specific wearOS case.

Bug: 285631818
Test: atest WallpaperManagerTest
Test: put logs and check visibility events
Change-Id: Icb63e3291c342fede3d601e084b192cb5a7d9b04