New strings for granting foreground to background perms

When an app has foreground only-access and requests
background access the grant dialog becomes more clear.

Logic regarding the labels on the buttons and which buttons
are visible is moved to GrantPermissionsActivity by passing
a CharSequence array into updateUi and using null to mark
button as gone.

Test: Open Grant Dialog in various cases
      atest CtsAppSecurityHostTestCases:android.appsecurity.cts.PermissionsHostTest
Fixes: 125416102
Change-Id: I8585d45945e87e5a8fbc6fe53bedf7827778d959