fix #16842: alignment of winged repeat barline

[futamapapa]

Resolves: #16842

The root cause of the issue is that, for end repeat barlines, the repeat dot is used as the origin of the X coordinate, causing the bounding box to extend beyond the right edge of the barline.

I updated the calculation of the horizontal offset w1 for reversedBracket, which was previously fixed to 0, so that it is computed correctly when a wing is present.

In TLayout::layoutBarLine:
w1 is calculated as the difference between the width of a repeat barline without wings (w) and the width of the wing (font->width(SymId::reversedBracketTop, magS)).

In TLayout::layoutBarLine2:
Since bbox.x() already accounts for this offset, w1 is obtained as the difference from item->symBbox(SymId::reversedBracketTop).x(), which does not account for the offset.

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[Jojo-Schmitz]

wanted for 4.7?

[miiizen]

No thanks, we're limiting PRs to regressions & what's already in the project at this point