Load monochrome app icon in SBIV

Previously, we were resolving the drawable just to check if we have a
monochrome version of the icon, and then resolving it again in SBIV. Now
we're only doing it once.

Bug: 335211019
Test: manually tested a few apps
Flag: android.app.notifications_use_monochrome_app_icon DEVELOPMENT
Change-Id: Id3eb0aa9098fd8a073faa1c063c72c91e0dd145b