Update storage permission policy to use AppCompat APIs.

This CL introduces ENABLE_SCOPED_STORAGE and REQUIRE_SCOPED_STORAGE as
AppCompat changes that are enabled for apps with targetSDK > P and apps
with targetSDK > Q respectively.

This change removes the getMinimumTargetSDK method, as it
is no longer needed.

Change-Id: I6b05252d42d3b2f1030928ffd03c02523c5a01d2
Fix: 147034231
Bug: 144914977
Bug: 131432978
Test: atest RestrictedPermissionsTest
Test: atest RestrictedStoragePermissionSharedUidTest