Do not consider "desktop" displays as fixed orientation

The current logic breaks public trusted virtual displays not
created with VDM, even if FLAG_ROTATES_WITH_CONTENT is
explicitly specified.

Additionally, isPublicSecondaryDisplayWithDesktopModeForceEnabled
should return "false" for virtual displays in general, because
the freeform windowing mode also breaks orientation requests from
activities running on these displays.

The new logic in isPublicSecondaryDisplayWithDesktopModeForceEnabled:
  - return false if FREEFORM is not supported on this display. This
    automatically includes all VDM displays because VDM doesn't
    support this windowing mode (for now)
  - return false for virtual displays without system decorations
    support (to allow virtual displays to explicitly opt-in - this API
    is hidden, and we can expose a different API in the future)

Fix: 407786865
Test: atest VirtualDisplayTest
Test: presubmit
Flag: EXEMPT bugfix

Change-Id: I42049d7f9b17eb365269fe8e25c7a64b289cd446