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).

ANSWER_PHONE_CALLS has also been made runtime-only.

Bug: 30932767
Test: cts-tradefed run commandAndExit cts-dev -m CtsPermission2TestCases
Change-Id: I42b30414c808730f2d5961ca31b6e3db740b8cf7