Add ReferenceObject metadata to improve DAC search

This adds some of the ReferenceObject fields listed here: https://developers.google.com/devsite/reference/microdata/referenceobject

It does not add the platform or version fields:
* A version could be added using the addedIn version of apiSince, but that doesn't seem particularly useful for AndroidX. It might make sense to do for Android if they switch to dackka.
* From my testing, only one `platform` value is used by devsite search if multiple are provided on a page, so platform wouldn't be useful for KMP.

Functions and properties are added as `property` fields using the generated anchor which is also the `id` for the item detail, because that should allow search to directly link to the item (though it currently does not, b/329124554).

Bug: 145282861
Test: Added component tests, updated integration test outputs.
Change-Id: Ifedb26fef9d06f196bebff0a0587485e7470a745