Simplify support of prefetch with data set changed after layout

Fixes: 33196708
Bug: 33077209

Switches setDataSetChangedAfterLayout to mark holders as invalid
immediately, so that invalid but stable-id views can remain in the
cache, as expected by an adapter with stable ids.

Also adds a stable ID sample to support v7 demos.

Change-Id: Ibcfbc1f7376d3585872ec32df2d2026137419296
4 files changed