Flip all scale based widgets to use scale denominators instead
of actual scales (ie 100.0 instead of 0.01 for 1:100).
This is done for consistency with the rest of the API, which
predominantly uses scale denominators. It also helps
precision loss as a result of multiple 1.0 / scale conversions
throughout the code.
Refs #15337
Rationale:
- there was a lot of large objects passed by value, so potentially
there's a speed bump from this
- even for implicitly shared classes like QString/QList there's still
a (small) cost for copying the objects when there's no reason to
- it's the right thing to do!
