[Plugin API] Add Action for adding simple lines/textlines

Your idea

With the latest MuseScore build, spanners are now exposed through the plugin API, which is a great improvement and enables more advanced plugin workflows.

However, not all spanner types are currently accessible via actions, meaning they cannot be created programmatically using cmd() from a plugin. In particular, there is no action available to add a simple line (referred to as “Text line” in the Properties panel).

Problem to be solved

For my instrument, standard notation is not sufficient. Instead, we use a system called Griffschrift, which indicates:

• which button to press
• whether to push or pull the instrument

The push/pull direction is represented by a line underneath the staff.

These lines need to:

• start at a specific note
• extend precisely to the end of another note’s duration

Current Limitation:
Using currently available spanner actions (e.g. Ottava lines like add-8vb) does not work correctly for this purpose, since they cannot span across the full duration of the note in the required way

Request
Please expose an action (e.g. add-textline) that allows plugins to create text line spanners programmatically, since they span across the full duration between notes.

Prior art

No response

Additional context

No response

Checklist

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