Support non-numerical id (with prefix) for virtual camera

This will ensure that virtual camera id's don't clash
with camera id's provided by any other HAL's. Also, this
should be fine as we currently don't expose virtual camera
id's to apps.

Test: atest CtsVirtualDevicesCameraTestCases
Test: atest virtual_camera_tests
Test: atest CtsVirtualDevicesCameraCtsTestCases
Flag: android.companion.virtual.flags.virtual_camera
Bug: 343404629
Change-Id: I304161eee08b144b82d31e8e9b8a9fcc2b9fc45c