SF: Propagate uniqueID when creating virtual displays

This is part of Trunk Stable effort to upstream SF-ARC screen record
capabiliy (undiverging http://ag/20003031) which requires mirroring
virtual displays to be associated with screen capture sessions using
the package name within the unique ID.

Creating virtual display with unique ID specified is optional such that
it doesn't affect existing consumers who don't need it (i.e. av).

Bug: 137375833
Bug: 194863377
Test: libsurfaceflinger_unittest
Change-Id: Ia3cd13df07f701593ddc94c196df0b04844cf502
diff --git a/services/surfaceflinger/DisplayDevice.h b/services/surfaceflinger/DisplayDevice.h
index edd57cc..543a16a 100644
--- a/services/surfaceflinger/DisplayDevice.h
+++ b/services/surfaceflinger/DisplayDevice.h
@@ -329,6 +329,7 @@
     uint32_t width = 0;
     uint32_t height = 0;
     std::string displayName;
+    std::string uniqueId;
     bool isSecure = false;
     bool isProtected = false;
     // Refer to DisplayDevice::mRequestedRefreshRate, for virtual display only