[AU4] limiting wave drawing to the visible area

au4/src/au3wrap/iau3wavepainter.h

au4/src/au3wrap/internal/au3wavepainter.cpp

...ectscene/qml/Audacity/ProjectScene/clipsview/ClipItem.qml

...e/qml/Audacity/ProjectScene/clipsview/TracksClipsView.qml

au4/src/projectscene/view/clipsview/clipslistmodel.cpp

au4/src/projectscene/view/clipsview/timelinecontext.cpp

au4/src/projectscene/view/clipsview/timelinecontext.h

au4/src/projectscene/view/clipsview/waveview.cpp

au4/src/projectscene/view/clipsview/waveview.h