add courtesy keysig to last measure even if it is followed by frame

[sammik]

Resolves: #22256
Resolves: #19759

• creating courtesy keysig was disabled by MeasureLayout::createEndBarLines(measure, **false**, ctx);, which sets ElementFlag::KEYSIG of measurebase to false, so before adding trailer, we need to re-createEndBarLines with truthy isLastMeasureInSystem value
• this was already (almost) done, with one exception - it processed last measureBase of system, but we need last real measure (not frame)

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[Jojo-Schmitz]

What about section breaks?

I don't think courtesy key sigs should show in that case, just like courtesy clefs and courtesy time sigs

Changing to

        if (ctx.state().prevMeasure() && ! ctx.state().prevMeasure()->sectionBreak()) {
            MeasureLayout::createEndBarLines(lm, true, ctx);
        }

fixes that, I'll PR this, see #25865

[sammik]

What about section breaks?

Thank You, I missed this.