[dev_option] Update strings for freeform window toggle

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

Test: EXEMPT string change
Bug: 348193756
Bug: 348186127
Flag: EXEMPT refactor

Change-Id: I8b61cd022b74980514a853eb9d462864c2b6b3e5