Add configurable scaling for wallpaper zoom

Configuration for minimum scaling is added to allow the
scale to go below 1.

[WearOS Upstream]
To upstream the cherry-picked CL from Wear into Android main, the
following changes were made to the original CL:

1. Added set* methods for test instrumentation.
2. config_alwaysScaleWallpaper was removed in favor of the solution
discussed in go/upstreaming-watchface-scaling

Bug: 172288002
Test: atest WmTests:WallpaperControllerTest
Test: atest WallpaperServiceTest
(cherry picked from commit ef8b62498b2615b524c2a3b79e021b20f52ffbac)
Change-Id: Iee711f702ab65ee4adf8e5b06764482a6fc7c6c9