[AOD RONs] Clean up view updater a little

Also, discard blank CharSequences and Strings in the extractor.

Bug: 402147652
Bug: 402510675
Flag: com.android.systemui.aod_ui_rich_ongoing
Test: NA, refactor
Change-Id: I3d09322e8a3a76f2cb173a733fb347a9a3a50969