Forgot to update Readonly `SpinBox`es to Qt 2 when implementing Cura
8684. As the spinbox is used in various places with the same
functionality it made sense to create a reusable component.
There is still a feature gap in the implementation; The `SpinBox`es
from QtControls 2.x value is defined as an integer. For some use-cases
we do require a fractional value in the `SpinBox`. The only two places
where this is required are the `material_diameter` and
`material_density` fields in the material prefference page.
Cura 8684
This was a weeeird bug. It worked if you changed the value and selected another field.
Pressing enter however (aka; The behavior that 80%+ of the users have) would change it
but it would switch back in half a second. It seems to have been caused by mutliple onEditingFinished
signals being emitted in sequence.
As I can't be bothered to go through the bowels of QML and figure out why exactly this is doing what it's doing,
I just tied the enter to losing the focus, which ensures that the right behavior happens (Field is no longer selected,
and the onEditingFinished is emitted)
Contributes to CURA-6590
