QSpinBox and QDoubleSpinBox - add an option to setOverwriteMode

The same way as it is done in a QTextEdit; it would be nice to be able to set an overwrite mode in a QSpinBox and QDoubleSpinBox.

With setOverwriteMode(true) we would get for example:
When | is the cursor and we have
12|3
Typing a 4, would return the result:
124|