Merge "Document that this ResolverActivity isn't directly used." into udc-dev am: 45246ffd7d am: 0a2fca3d06

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/modules/IntentResolver/+/23209030

Change-Id: Icd20d710c8af48b1f1787484f4edc6f563ebb95f
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>