[wm] Adjust freeform header not to be overlapped with stable insets

freeform bounds should not be overlapped with statusBar and navigationBar.
If it is overlapped, we can't control freeform anymore. So we adjusted
freeform bounds not to be overlapped on launching and moving task.

Test: move freeform to navigationBar & launching below navigationBar
Test: atest WmTests:TaskRecordTests WmTests:TaskPositionerTests
Bug: 129521219
Change-Id: I353ba930269ec753c97d719819364436bda280cb
(cherry picked from commit 55fbe465f2b40e0f1886691488825a243a3acf79)