Create and use peekBitmapDimensionsAsUser in ImageWallpaper

Exactly like ImageWallpaper uses WallpaperManager.getBitmapAsUser, it
should specify the userId when peeking the bitmap dimensions. This is
because SystemUI's context.getUserId() returns 0 in HSUM mode, even if
the current user is the user 10, resulting in wrong bitmap dimensions.

This is fixed under flag: without multi-crop, setting an zoomed image on
tablet seems broken regardless of whether this fix is included. Thus, it
felt more logical to include this fix in the multi-crop flag and ignore
the previous version.

Flag: com.android.window.flags.multi_crop
Test: manually verified the HSUM bug
Bug: 358567206
Change-Id: I1e5ca70a0f5331f6bca55baf9c66296531cee5d8