[RONs] Move permission enforcement under ui_rich_ongoing.

Enforcement must be checked as soon as RONs are released.
But, leave visible API under api_rich_ongoing_permission flag,
to be turned on for Q4 release.

Test: Manual verification; existing CTS tests
Bug: 417260729
Flag: android.app.ui_rich_ongoing
Change-Id: Ie7b428631602a00c2bde13a2bf31ef779f1f7a15