docs: Mention app query filters on Android 11

For apps that target Android 11 and higher, the methods in this class
each return a filtered list by default, because of the new package
visibility behavior.

Test: m ds-docs-java

Bug: 173104139

Exempt-From-Owner-Approval: Docs-only change
Change-Id: Idd239a6a9b4e1764b8285f73a341adc024281be2