SF: Remove *DisplayId::tryCast and DisplayId::isVirtual()

Work towards DisplayId opaqueness by eliminating call-sites to APIs that
parse the display ID values directly.

This CL removes *DisplayId::tryCast from the DislayId interface entirely
and replaces it with SF APIs that check for the existence of the
displays before casting. This removes direct dependency on ID value
bits. It also removes DisplayId::isVirtual().

Flag: com.android.graphics.surfaceflinger.flags.stable_edid_ids
Bug: 390690584
Bug: 390689313
Test: libsurfaceflinger_unittest
Change-Id: I918a6b361784e41165837234b82eed027dc46673