Refactor IndexData conversion flow

This is entirely implementation detail, the public
interface and tests get to stay the same.

- The Raw, Resource and Provider methods now return single
or lists of IndexData rather than adding to a member var.
- Some code duplication was removed for Raw IndexData.
- Extra methods were squashed or removed

The only remaining refactoring in IndexDataConverter is
moving work done on IndexProviders to get the raw and
resources into PreIndexDataCollector.

Bug: 33577327
Test: make RunSettingsRoboTests, Database dump before & after
Change-Id: If6011046955f242ba2614400cfeca3bea5b683cb