Consider enforce property for desktop mode

Commit 813cfb25 separated the condition to check display, but it
becomes always enforced the real device condition. Then even if
developer option is enabled with the property set, there is still
no app handle and caption bar when togging windowing mode from
overview menu.

Bug: 384568161
Flag: EXEMPT TEST_ONLY
Test: On a phone device.
      Enable desktop experience on developer options.
      adb shell setprop \
      persist.wm.debug.desktop_mode_enforce_device_restrictions false
      The app handle will show on task.
Change-Id: I16f0c3d971acaae50767e41b67ebafc156beca11