Selection by subtype for many more elements

[XiaoMigros]

This PR allows selection by subtype of elements where it previously wasn't possible. Additionally it resolves: #23019

For example, the subtype option for key signatures was previously grayed out. Now, it's possible to select them based on key:

• [x] I signed the CLA
• [x] The title of the PR describes the problem it addresses
• [x] Each commit's message describes its purpose and effects, and references the issue it resolves
• [ ] If changes are extensive, there is a sequence of easily reviewable commits
• [x] The code in the PR follows the coding rules
• [x] There are no unnecessary changes
• [x] The code compiles and runs on my machine, preferably after each commit individually
• [ ] I created a unit test or vtest to verify the changes I made (if applicable)

[its-not-nice]

There are quite a few text types (Tempo, Rehearsal mark, Bar number, etc) where there's only one subtype, i.e. the subtype matches the element type. In these cases the 'Same subtype' checkbox feels redundant.

It feels strange to me that the element type and subtype fields look like text boxes but aren't editable:

Whereas the info shown for notes, for example, is just plain text:

Which is less misleading to me (unless I'm missing something)

[XiaoMigros]

There are quite a few text types (Tempo, Rehearsal mark, Bar number, etc) where there's only one subtype, i.e. the subtype matches the element type. In these cases the 'Same subtype' checkbox feels redundant.

For text based elements (outside of this PR as well), the 'subtype' property is actually just the text style type. What do you think of this option dynamically renaming itself, in this case to 'Same text style type'? For the example above 'Same key' could work too

[cbjeukendrup]

It looks like some overrides of subtype() and subtypeUserName() are missing the override keyword, causing some compiler warnings. Would be good to fix those

[Jojo-Schmitz]

And a rebase is needed

[cbjeukendrup]

A merge commit has appeared; that probably means that you accidentally pulled instead of force-pushed. A rebase will probably fix it.

[XiaoMigros]

Yes, rebases have done the trick so far, but they only seem to squash the commits if there have been changes made to master since then. Thanks for the pointers and extensive feedback, it's been really helpful :)

[XiaoMigros]

All thanks to your help!