feat: improve cursor behaviour during digitization

[merydian]

The map cursor will now be a pointing finger when dialog is visible. Also, the cursor is no longer set application wide, but within the maptool class.

[koebi]

Hey,
great find that we can set the cursor for the tool, not the whole application!
I am not quite sure though why that changes the logic on setting/resetting the cursor? The current approach looks a bit like we never reset the cursor, i.e. adding and adding and adding to the stack?

[merydian]

As opposed to the cursor stack created by QApplication.setOverrideCursor(), there is no such stacking mechanism at the QWidget level. Each call to QWidget.setCursor() simply replaces the widget’s current cursor. See: https://doc.qt.io/qt-6/qwidget.html#cursor-prop

QgsMapTool controls a QgsMapCanvas instance, which inherits from QWidget, so this behavior applies here as well.