Breaking change in MPESynthesizerBase in juce 6.1.5

instrument went from std::unique_ptr<MPEInstrument> to MPEInstrument&. probably should add this to the breaking changes document?

This tripped me up too!

Got a bit of head-scratching refactoring to do to properly fix a resulting build error after this change…

This just messed my project up too… why is this still not in the breaking changes?!