Protect base types by delegating to a proxy implementation

Ie981b36e53220e4107d5194e95899e23ce16ffe0 introduced an issue where
custom clocks wouldn't render in Flexiglass due to the protection
layer generating and using a proxy of BaseLockscreenElement instead of
LockscreenElement or MovableLockscreenElement as appropriate. This
change fixes that issue by marking the base-interface differently and
resolving to the appropriate extending type proxy implementation based
on the runtime type information of the target object.

Bug: 441721558
Test: Checked custom clocks in flexiglass
Flag: com.android.systemui.scene_container
Change-Id: Ic3be9af34123f5bcd38c185817594632124169c5