Add the feature to lock measures per staff available in version 4.5

[Gtmanure]

Hi!

I'm a newbie, and I was advised to come here to make a suggestion for improvement. I've been sticking with MuseScore 3.5 because I use the MIDI features extensively, and I didn't know that the project was continuing in parallel, so kudos to the artists!

Recently, someone pointed out to me that a new feature was added with version 4.5, and it would be awesome if it could also appear in MuseScore 3? :p

The feature I'm talking about is the ability to lock the number of measures per staff. It's really useful for speeding up the editing process, especially since the measure width management system in MuseScore can be a bit clunky.

Anyway, it's just a simple suggestion ;)

Thanks to the team for continuing to develop version 3!!