Update display windowing mode when development settings change

Display settings load windowingMode from display_settings.xml, but check
the enable_freeform_support before setting the windowingMode to
freeform. As a result, we need to update the windowingMode when
enable_freeform_support change.

Fixes: 151163592
Test: WindowManagerSettingsTests
Test: manual: with setting freeform in display_settings.xml, was able to
      switch windowingMode by changing enable_freeform_support
Change-Id: I19a5bf61461926e88de94351d3ebe0fa8b96afb2