Use system cursors instead of embedded raster images where possible (#7838)

Given these changes, the knife tool now uses `Qt::SplitHCursor`, but `Qt::IBeamCursor` is also a a viable option. I am noting this should substantial concern arise over the appearance of `Qt::SplitHCursor` due to cursor themes, such as the default one applied to applications running under WSL.

data/themes/classic/style.css

@@ -734,10 +734,6 @@ lmms--gui--TimeLineWidget {
 
 	qproperty-barLineColor: rgb( 192, 192, 192 );
 	qproperty-barNumberColor: rgb( 192, 192, 192 );
-
-	/* Cursor hotspots for loop marker adjustment */
-	qproperty-mouseHotspotSelLeft: 0px 16px;
-	qproperty-mouseHotspotSelRight: 32px 16px;
 }
 
 QTreeView {
@@ -762,10 +758,6 @@ lmms--gui--ClipView   {
 	qproperty-textShadowColor: rgb( 0, 0, 0 );
 	qproperty-gradient: true; /* boolean property, set true to have a gradient */
 	qproperty-markerColor: rgb(0, 0, 0);
-	/* finger tip offset of cursor */
-	qproperty-mouseHotspotHand: 3px 3px;
-	qproperty-mouseHotspotKnife: 0px 0px;
-
 	font-size: 11px;
 }
 

data/themes/default/style.css

@@ -799,10 +799,6 @@ lmms--gui--TimeLineWidget {
 
 	qproperty-barLineColor: rgb( 192, 192, 192 );
 	qproperty-barNumberColor: rgb( 192, 192, 192 );
-
-	/* Cursor hotspots for loop marker adjustment */
-	qproperty-mouseHotspotSelLeft: 0px 16px;
-	qproperty-mouseHotspotSelRight: 32px 16px;
 }
 
 lmms--gui--TrackContainerView QLabel
@@ -823,10 +819,6 @@ lmms--gui--ClipView   {
 	qproperty-textShadowColor: rgba(0,0,0,200);
 	qproperty-gradient: false; /* boolean property, set true to have a gradient */
 	qproperty-markerColor: rgb(0, 0, 0);
-	/* finger tip offset of cursor */
-	qproperty-mouseHotspotHand: 7px 2px;
-	qproperty-mouseHotspotKnife: 0px 0px;
-
 	font-size: 11px;
 }