Implement initial policy for memory tag checks.

System apps and the system_server receive async tag checks, while all other
app processes have it disabled. Developers may enable async tag checks
per application with:

$ adb shell am compat 135772972 <app.name>

Bug: 135772972
Change-Id: I154623941eec8e79af347453fbca1b062346c85b
Merged-In: I154623941eec8e79af347453fbca1b062346c85b