Roll forward "Show error dialog if activity is blocked from streaming"

Added BlockedAppStreamingActivity to an "always allow" list so that it
can always be displayed even if no other activities are allowed. Also,
instead of reusing BlockedAppActivity, separated it out to a different
activity that doesn't have the lockTaskMode="always".

Bug: 203834118
Test: atest CtsVirtualDevicesTestsCases
Change-Id: I5f0b68cd8ac701847489130e6018ecafb1ebc4a8