Make documentLaunchMode="never" activity don’t create task

Activity that specify “documentLaunchMode="never" should not launched
into a new document even if the Intent contains
FLAG_ACTIVITY_NEW_DOCUMENT.

This CL overrides the behavior of the FLAG_ACTIVITY_NEW_DOCUMENT and
FLAG_ACTIVITY_MULTIPLE_TASK flags to make the definition consistent
with documentation.

Bug: 113840793
Test: atest IntentTests
Change-Id: I9b96e7fe0306d54b8f833873bcad8e0508dd3aa8