Ignore PendingResults when checking for mutable implicit PendingIntents

The mutable implicit PendingIntent check, introduced in U, accepts all
types of pending intents, however, pending intents of type
INTENT_SENDER_ACTIVITY_RESULT need to be ignored because they are
intrinsically tied to a target - they are already explicit.

Bug: 274078367
Test: atest PendingIntentTest
Change-Id: Ibb35c581af7aeb09dba3bf2bf0bf21a21b92a278