Add application level asm attribute

We are moving the Activity Security Model to an opt-in approach for V.
To facilitate this change, we introduce an application level
allowCrossUidActivitySwitchFromBelow manifest attribute, mirroring the
activity level flag we introduced earlier.

              Flag Type | Default |
	    |  -------  | ------- |
Application | Manifest  | true    |
Activity    | Runtime   | false   |

ASM will be applied if:

1. The top app in the stack has opt-ed in by setting the application
   level flag to false
2. The activity has not opt-ed out by setting the activity level flag
   to true.
3. Both the top app, and the app performing the launch, target at least
   V.

As part of this change we also clean up the feature flags as we were
previously using primarily mendel flags.

1. The trunk stable flag is now the primary control for the feature. If
   the trunk stable flag is off, feature enforcement is fully disaabled.
2. However logging and toasts can still be enabled for the droidfood
   population via a mendel flag.
3. If the trunk stable flag is enabled, it can be further configured to
   ignore target sdk levels for teamfood via mendel.

Bug: 322913638
Test: atest ActivitySecurityModelTest
      ActivitySecurityModelEmbeddingTest BackgroundActivityLaunchTest

Change-Id: I4668de42dc41a78778166aa053b723a36b49f32b