[MU4 Task] Implement cross-staff beaming button in note input toolbar

[bkunda]

Task description
This is a task to add a button for cross-staff beaming into the note input toolbar.

The button will trigger a context menu – much the same as the current behaviour for the tuplet button.

The actions will be identical to the current keyboard shortcut commands "move chord/rest to staff above" and "move chord/rest to staff below". We are not adding any new functionality to this feature at this stage.

Please see this Figma file for the full design spec: https://www.figma.com/file/l0TQUrNFZmEfrZnfHhFDfb/Musescore-Notation-App-MASTER?node-id=23179%3A569821

The relevant icon has been added to musescoreicon in position U+F43D

Let me know if you have any questions,
Thanks!

[HemantAntony]

I am attempting to work on this :)