Exclude extra navigation bar insets for floating windows

Extra navigation bar should be treated as navigation bar for floating
window and PIP window. It should not affect the content layout.

Bug: 160750722
Test: Add extra navigation bar from system UI, and launch a freeform
      window to test.
Test: go/wm-smoke
Change-Id: I145881e3e87f5f0ef0866ca5143121f76dc7dace