Support for gabc notation

Your idea

Musescore should add support for gabc Gregorian Chant notation, as created and open-sourced by the Gregorio Project.

Problem to be solved

The gabc standard is used for writing Gregorian Chant (see https://gregorio-project.github.io/gabc/). It's pretty well documented already, and fully open-source. Support for this notation standard inside MuseScore would a) be really awesome and b) instantly make MuseScore the standard way of writing Gregorian Chant (the extant open-source options are rather difficult to use, so there's a definite gap in user-friendly implementations here that I think MuseScore is ideally suited to fill)

Specifically, there are a large number of tools that can turn gabc files (which are ASCII-based) into a pdf, png, or similar, but I have not been able to locate a single tool that enables writing the chant in a GUI and then exporting the gabc. This makes it very very difficult for people to write Gregorian Chant without first learning how to write the notation files in a text editor! MuseScore already has extensive code dedicated to arranging note-objects on staves that I think could be repurposed fairly easily to write Gregorian Chant.

Prior art

No apps that I am aware of enable writing Gregorian Chant in a GUI and exporting that to .gabc.

The following apps convert .gabc files into graphical notation:

https://bbloomf.github.io/jgabc/transcriber.html

https://run.gregoriochant.org/cgi/process.pl

https://www.sourceandsummit.com/editor/legacy/

This is the homepage of the project:

https://gregorio-project.github.io/gabc/

Additional context

No response

Checklist

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Start by reading the gabc standard and reviewing MuseScore's existing note-object and staff-arrangement code, which the issue identifies as potentially reusable. Define the scope for GUI chant authoring and gabc export; done means a user can create Gregorian Chant notation in MuseScore and export it as a valid .gabc file.