Fix sharing bugreports from lockscreen

When launching ChooserActivity from lockscreen, we will start it
in stopped state because lockscreen is still showing, meaning that
the activity goes through start -> resume -> pause -> stop
immediately after it was launched, and will be later resumed once
Keyguard actually goes away.

However, ResolverActivity finished itself in onStop. We add a
private extra to change this behavior for sharing bugreports.

Test: Take bugreport, double tap on it on lockscreen
Test: com.android.shell.BugreportReceiverTest$1
Bug: 33009364
Change-Id: I973b2c71587950499b7c88b16af9cf1387795e17