Make sure activity is started in requested windowing mode

An existing activity was brought to front, but was not launched in
requested windowing mode because the task was simply reused without
updating to the preferred windowing mode.

Bug: 177190100
Test: atest WindowMetricsActivityTests#testMetricsMatchesDisplayAreaOnFreeformActivity
Change-Id: I43884c3297995e536e91a81bbb0c290da7aace1c