Don't show unsupported sdk warning in test harness.

Also, added test api AM.alwaysShowUnsupportedCompileSdkWarning
that allows for forec showing the warning for an activity
component running in a test harness.

Change-Id: I72f6a8425cb6adc6060c70b2165aa82b459769f7
Fixes: 75455658
Test: atest CtsActivityManagerDeviceTestCases:PrereleaseSdkTest