Shortcut to increase/decrease all dynamics in selection by one step

### Your idea A shortcut that increases every dynamic marking by one step (eg, every mf becomes ff, every ff becomes fff). And one that does the opposite. Up for discussion how many p's and f's it goes to, and how it interacts (if at all) with hairpins (eg, does increasing the end of a mf > mp by two clicks change it to a mf < f or leave it as mf > f). ### Problem to be solved I'm not aware of any convenient ways to modify dynamics using keyboard. It's a pretty common need (for me at least) to want to tweak dynamics. When there is just one stave affected, it's not too bad: click the dynamic, click the new dynamic from the popup menu. But when there are multiple staves (eg, 4 trumpets in a brass section), it's tedious: either repeat this process for each stave, or use clunky workarounds to select and delete all the existing dynamics, then create new ones. A mechanism like "increase by one step" is very flexible, because you can intuitively use the same tool to replace all p's with ff's simply by pressing the same keystroke a few times. I think it would be less common to increase/decrease dynamics that are different within the same selection (eg, bumping a p and an f to mp and ff) but not problematic, and still intuitive. ### Prior art _No response_ ### Additional context _No response_ ### Checklist - [x] This request follows the <a href="https://github.com/musescore/MuseScore/wiki/Reporting-bugs-and-issues" target="_blank">guidelines</a> for reporting issues - [x] I have verified that this feature request has not been logged before, by searching the <a href="https://github.com/musescore/MuseScore/issues" target="_blank">issue tracker</a> for similar requests