Set windowing mode in TDA instead of DisplayContent

Set the windowing mode in TaskDisplayArea. Earlier found that because
the windowing mode is set in DisplayContent, all WindowContainres under
the DisplayContent will inherit the new windowing mode. However, for
system windows, their windowing mode should always been fullscreen.
Setting the windowing mode in TDA can fix the issue. Using this new
method instead of resolving the system window windowing modes in
WindowToken.

Bug: b/241168290
Test: services/tests/wmtests
Change-Id: I3876020cf06f6bfe6d88431bc3609c7a67c833fc