Add support for section restart to MEI import

[rettinghaus]

This PR adds support for MEI's section@restart to the MEI importer.

(Also it removes an outdated comment I overlooked in #22943.)

[cbjeukendrup]

The following would be more MuseScore-idiomatic:

Suggested change

	Measure* measure = dynamic_cast<Measure*>(m_score->measures()->last());
	if (measure) {
	MeasureBase* mb = m_score->measures()->last();
	if (mb->isMeasure()) {

Alternatively, at the start of the method do:

MeasureBase* lastMeasureBase = !m_score->measures()->empty() ? m_score->measures()->last() : nullptr

and then check if (lastMeasureBase) or lastMeasureBase && lastMeasureBase->isMeasure() where appropriate (also at the bottom of the method)

[rettinghaus]

@cbjeukendrup Thanks, looks more elegant now. But unit test fail. Any idea?

[cbjeukendrup]

Ah, I think I see the potential problem: what's the last measure at the top of the method, might not be the last measure anymore at the bottom of the method. In between, this->readMeasure for example might add another measure.

So, it looks like you inevitably need to query the last measure twice.

[rettinghaus]

Of course, you're right. I reverted the latter change, so now it should be good to go.