Fix #304843 - Brackets displaced in Continuous View

[njvdberg]

Resolves: https://musescore.org/en/node/304843

Call to layoutSystem() in Score::collectLinearSystem() didn't take the existence of a HBOX into account. Instead of fixed 0.0, now the shift due to the HBox is passed.

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• I created the test (mtest, vtest, script test) to verify the changes I made