Use a separate code path for rich content in augmented autofill

Image suggestions (and other rich content) are not handled the same way
as primitive autofill values. These suggestions are also only applicable
to augmented autofill. Therefore, instead of reusing AutofillType and
AutofillValue, we use a separate code path to insert rich content. A
follow-on change will remove AUTOFILL_TYPE_RICH_CONTENT and the
corresponding code on AutofillValue.

Bug: 168837034
Test: Manual and unit tests
  atest CtsAutoFillServiceTestCases:DatasetTest
  atest CtsAutoFillServiceTestCases:InlineAugmentedAuthTest
  atest CtsAutoFillServiceTestCases:InlineAugmentedLoginActivityTest
Change-Id: I4fa3baf2b545908fc25f3a6e28a7addc7004786b