Keep legacy permission granted if it has been reviewed.

IMPLICIT is the new flag we use for REVIEW_REQUIRED and
REVOKE_WHEN_REQUESTED, and if a permission for a legacy app no longer
has it, we should keep it as granted with RUNTIME_GRANTED when
dropping LEGACY_GRANTED.

Fixes: 284366779
Test: atest PermissionFlagsTest RestrictedPermissionsTest
      RestrictedStoragePermissionTest SplitPermissionTest
      PermissionReviewTest PermissionTest22 PermissionUpgradeTest
Change-Id: If967e41d0e90e61663b6694050af1b57a01c9825