Ensure that display settings fallsback to DApolicy

- currently windowing-mode set on default tda is overridden by the
  one coming from the display_settings.xml (after its resolved by
  checking freeform support and falls back to fullscreen)
- with this change it will instead fallback to the one that is
  already set in the defaultTDA which comes from the Policy.

Flag: EXEMPT bugfix
Bug: 348677823
Test: atest DisplayWindowSettingsTests
Test: Tried out by setting a custom DaPolicy
Change-Id: I8c77fbb7ef8b5b84df4b7fda1e3dd3e33234b391