[Dev options] Conditionally show Freeform toggle: Only display when freeform...

[Dev options] Conditionally show Freeform toggle: Only display when freeform is NOT available by default on the device.

Previously Freeform Toggle was a no-op when freeform was by default available on devices

On the other hand Desktop mode toggle is displayed only when freeform IS available by default on the device. (This is because desktop mode support is tied to devices with default freeform capability.)

Also update toggle strings for a clearer user experience

Test: Updated tests
Bug: 348193756
Bug: 348186127
Flag: com.android.window.flags.show_desktop_windowing_dev_option
Change-Id: I29e36a939db78010bb3153e756f95bb6c21a31f9