Alert Windows behavioral changes

- Introduced TYPE_APPLICATION_OVERLAY window type. Can be used by apps
to display windows on top of other app windows, but below critical
system windows.
- Deprecate alert window types TYPE_PHONE, TYPE_SYSTEM_ALERT,
TYPE_SYSTEM_OVERLAY, TYPE_PRIORITY_PHONE, and TYPE_SYSTEM_ERROR.
Apps should now use TYPE_APP_OVERLAY for this.
- Apps targetting O or greater are not allowed to add the old alert
window types.
Apps targetting less than O can still add the old types.
Apps with permission INTERNAL_SYSTEM_WINDOW (system signature apps) can
still add the old types.
- Z-order old alert windows types below TYPE_APPLICATION_OVERLAY if
they are added by an app without the INTERNAL_SYSTEM_WINDOW permission.

Test: android.server.cts.AlertWindowsTests
Bug: 33256752
Change-Id: I12170955a7a333151d3387c169b51c53c32164fc