Expose pending request to subclasses and ensure clean up

Pending requests were not exposed to subclasses interested in
operating on them and also the pending requests were not cleaned
up after being handled leaving them in memory and potentially
preventing us from unbinding from the remote service upon timeout.

Test: Perform the following steps on a Meta Quest 2:
1. Launch 2D app in shell
2. Launch 2D app in shell from non activity context
3. Launch 2D app in shell and request permission in 2D
4. Request permission from 3D app in 2D overlay
5. Request permission from 3D app in 2D (via VrUi)
6. Subclasses can access pending jobs which are cleaned upon completion

Change-Id: I29e7146619913dd3457fa2a228cece2d245ff02d