Populate iconResId in ModesTileModel if it's know to be a system icon

Also, ModesTileMapper now always lets the iconResId through if populated, even with modes_ui_icons on.

Bug: 360399800
Test: atest ModesTileDataInteractorTest ModesTileMapperTest
Flag: android.app.modes_ui
Change-Id: I59d10e2180837a09e33959c4a2c67949bbe505c0