[AOD RONs] Use packageContext instead of SystemUI context

This fixes an issue with fetching the app icon, but also allows us to do
other things with the context (like obtaining the profile badge, see
follow-up CL).

Bug: 414830446
Bug: 402147648
Test: post RON from app only installed on work profile, verify it doesn't crash
Flag: android.app.ui_rich_ongoing
Change-Id: I4be70d14603e631ae0aba3f627b765f318027fd6