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: Ie7d2fa637d741623763a070000696d4d95215b4d