In the export dialog(s) have a button to export all parts of a score that have corresponding open tabs

Your idea

In addition to "Select all" and Empty selection" there should be a "Select all open" or maybe a "Select all generated", although the latter won't make much sense without the ability to really get rid of the generate ones (see also #26878), or to differentiate the automatically generated 'single' ones from 'manually' created ones (often containing more than one onstruiment)

Problem to be solved

I often use manually created parts to separate Choir (Closed score SATB, 2 'instuments'/parts, women and men) from the band or orchestra (e.g. Piano, Flute, Bass).
On export I then usually want the main score and those manually created parts as PDFs, while e.g. a single part for men (Tenor/Bass) usually doesn't make any sense (the lyrics are usually attachetd to the women, Soprano/Alto staff only anyway).
Having to lookf cor and tick multiple boxes rather than just one button is a bit of a nuisance
The ones currently open are much more likely the ones I'd want to export (and I guess I'm not alone there), so such a button would come quite handy.

Prior art

In Mu2 and Mu3 parts had to get generated first, then show in the export dialog. So there are none I don't want (or if there are they are easily deleted).
In Mu4 however, parts apart from manually created ones are auto-generated as needed, but those may not be the ones you really want exported, actually in the presence of 'hand made' parts they rarerly are.

Additional context

Came up in #30685

Checklist

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Start by locating the export dialog or dialogs and the existing part-selection controls, then trace how currently open tabs are identified. Done means adding a control that selects the score parts with corresponding open tabs without changing the existing Select all or Empty selection behavior.