Add @UnsupportedAppUsage annotations

For packages:
  android.appwidget

This is an automatically generated CL. See go/UnsupportedAppUsage
for more details.

Exempted-From-Owner-Approval: Mechanical changes to the codebase
which have been approved by Android API council and announced on
android-eng@

Bug: 110868826
Test: m
Change-Id: Idbddc50320e7df92e0f260c1e309e5390b502d28