Add methods to VirtualDeviceManagerInternal

These allow determining:

-Which VirtualDevice's, if any, have a given app running on them
-What app owns a VirtualDevice

This information is going to be used for implementing siloed clipboard
support for VirtualDevices in ClipboardService.

Bug: 262038440
Test: atest VirtualDeviceManagerServiceTest
Change-Id: I78ee1c3ea1f21804b5f2faca4108c33156b27bc8