Fix #26411 Don't disable inspector controls based on value difference

I think (and have written in #26411) the way visibility flag is enabled and disabled is counter-intuitive.
Checking the code I discovered that also the "reset" button's behavior is strange (e.g. you can't reset the value of multiple selected items if they have the same value).
I believe removing the value difference check makes the best result in general and would make MuseScore work similar to other software. In special cases further enhancements could be made later (e.g. 3rd state for checkboxes).