Hide "Pending" APIs based on feedback.

We've been advised that the current API design strategy is to
implement new APIs in the support library, and leave the core OS to
be bare minimal APIs.

Bug: 126636931
Test: atest cts/tests/tests/provider/src/android/provider/cts/MediaStore*
Change-Id: I9488f0fd789bab08cd376f86056badcbcfb6cc2e