Add property for apps to request support for showing multi-instance entry points

- Currently, this is controlled by an allow-list, but we want to ensure
  that all apps can request to be launched in multiple instances in
  cases where SystemUI desires

Bug: 262864589
Test: atest WMShellUnitTests
Change-Id: I3d30132ddb3613560d4a8ecb28d4ea41aac9fe3b