Allow permissions to be runtime-only.

This adds the new runtime protection level flag that if set means
the permission can only be granted to apps that target runtime
permissions (>= M).

Bug: 30932767
Test: cts-tradefed run commandAndExit cts-dev -m CtsPermission2TestCases
Change-Id: I8792dc2b03276155a86e0d4db471205d169dd1ca