Merge "Add details about theme stability" into sc-dev am: 9aff8397c8 am: a35809b1a4 am: 9b578bf0db

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/16176790

Change-Id: I586f3a079128bb2039de552ba7d29a23e4b9b45f