Prevent toast being shown on a display that cannot host tasks

When a connected display is mirroring, Display.canHostTask() returns
false. In this CL, if a toast widget's target display is mirroring, it
will instead be shown on the default display.

Bug: 417098352
Flag: com.android.window.flags.enable_mirror_display_no_activity
Test: presubmit
Change-Id: I800b527537314dce8245c2fb9ba8c90d59096a07