OMS: rebase settings when overlays update

When an overlay package has been upgraded, OMS needs to reconcile any
previous settings about the overlay with the new state of affairs.
Sometimes it is possible to rebase the OMS settings on the new
information [e.g. the overlay has changed categories]; sometimes the OMS
settings have to be scrapped [e.g. the overlay has changed target
package]. Update OMS to do The Right Thing.

Bug: 78809704
Test: manual (adb shell stop, adb push specially prepared overlays, adb shell start, adb exec-out cmd overlay dump)
Test: ran unit tests
Test: adb install out/target/product/walleye/data/app/SettingsUnitTests/SettingsUnitTests.apk
Test: adb shell am instrument -w -e class com.android.settings.display.ThemePreferenceControllerTest com.android.settings.tests.unit/android.support.test.runner.AndroidJUnitRunner
Test: NOTE: 3 of 4 failures both pre and post change; looks like there are issue with the unit tests themselves

Change-Id: Icd1ae633dbee5b5ca957fa6b652af6209b4b1260