Moved isAppForeground to ActivityManagerInternal.

Removed isAppForeground from the ActivityManager aidl and added it to
ActivityManagerInternal. Updated all of its references as well.

Bug: 119327603
Test: atest cts.tests.app.src.android.app.cts.ActivityManagerTest#testIsAppForegroundRemoved
Test: atest WifiServiceImplTest
Test: atest WifiLockManagerTest

Change-Id: I5c0fbe41df3cd00e02f8c0e1005fc9cf5832df77