'Musical Symbols Scale' for markers

[XiaoMigros]

Resolves: #21757

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[XiaoMigros]

I wonder if it's possible to check for Sid::dummyMusicalSymbolsScale being used, rather than to use a chain of ORs...

[cbjeukendrup]

In the VTests, it looks like this has an undesired effect for existing scores (it makes those symbols much larger). Maybe some compat code is necessary to reset things in pre-4.4 scores?

[XiaoMigros]

In #20934 there were similar consequences (notably for pedal markings), but last time discussing with @oktophonie the conclusion was made that the symbols should now default to their 'true' size, regardless of context.

[cbjeukendrup]

I tested it and found that the look of existing scores is indeed affected, but in such way that these scores look the same as when you'd create a new score in this PR's build. So that does make sense to me :)