[1/n] Isolate desktop entry point disabling heuristic from window exemptions

The windowing exemptions logic is used for both exempting apps from
opening in desktop but also hiding the entry point so apps cannot be
moved into desktop. However, disabling desktop entry points is not
constrained by the same security restrictions as exempting apps from
opening as freeform in desktop. Instead we should have a separate
heuristic for disabling entry points and forcing to fullscreen.

Flag: EXEMPT Refactoring
Fixes: 407704088
Test: atest WMShellUnitTests:DesktopModeCompatPolicyTest,
      atest WMShellUnitTests:DesktopTasksControllerTest,
      atest WMShellUnitTests:DesktopModeWindowDecorViewModelTests
Change-Id: I802c0b676271fea9c88ace28619e429a6f9311e0