Fix Launcher preview display size

When previewing the Launcher in the Wallpaper Picker for a different
display size than the current screen, the preview no longer adapts to
that screen size.

Flag: ACONFIG com.android.wallpaper.multi_crop_preview_ui_flag DEVELOPMENT
Bug: 316000567
Test: manually verified
Change-Id: Ib10f2c9acec98ed99cadd40a588e2ffdea900ba6