[dev_option] Update 'Desktop mode on secondary toggle' to be

'Freeform windows on secondary diplay'.

Make sure the toggles enables freeform support on devices. This remove
reliance on 'Enable freeform windows suppport' toggle when using this
toggle.

Also update strings for all toggles to just use term 'freeform windows'
instead of 'desktop mode' or 'freeform windowing experiences'.

Two toggles have the same name 'enable freeform windows', but users will
see only one of them at a time.

Test: Added new tests
Bug: 348193756
Bug: 348186127
Flag: EXEMPT minor change
Change-Id: Ic4528618e6902d084c58a6b5ddeb4b92d63386d6