Stop using windowOptOutEdgeToEdgeEnforcement in CtsWidgetTestCases

Instead, this CL sets fitsSystemWindows to true to the content view.

Fix: 346688954
Bug: 309578419
Flag: com.android.window.flags.enforce_edge_to_edge
Test: atest CtsWidgetTestCases
Merged-In: I45128cf534c795c810de7f80cac96ff99e52e261
Change-Id: I45128cf534c795c810de7f80cac96ff99e52e261
(cherry picked from commit 47e1078d99767d0c0d51976848fda38d81e04457)