Update ASM rules based on feedback.

This change updates the rules based on droidfood findings.

1. BAL_ALLOW_SAW_PERMISSION now allows ASM bypass for new tasks. Some
   apps (i.e, alarm apps) use display over other window permissions to
   show the alarm activity even if the alarm task is not in the
   foreground. As users must explicitely grant this permission, we do
   not consider it a risk.

2. BAL_ALLOW_VISIBLE_WINDOW now only allows ASM bypass for new tasks. If
   an app requires a bypass within a task, it can request the new flag
   we are introducing in ag/20882611.

3. Do not clear activities from top of task if launcher or launched
   activity matches top activity. This is relaxed rule from before,
   where only the launched was considered. We allow this to allow
   pending intents to be passed from A to B in the case below, and still
   fired from A without creating unpredictable back behaviour. As A
   passes the intent to B (and launched B), we assume there is a
   level of trust between A and B.

B
A
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Bottom

Bug: 263368846
Test: atest BackgroundActivityLaunchTest ActivitySecurityModelTest
Change-Id: Ic698d27b35023063f3c7214414bee2b9298f4fb3