Opensheetmusicdisplay: Display Multi-Measure rests

[sschmidTU]

Added to Vexflow in November 2018 (PR 671).
https://usermanuals.musicxml.com/MusicXML/Content/EL-MusicXML-multiple-rest.htm

Currently, we render these measure for measure, because they are also still given like that in XML.
The starting multi-measure rest bar just has an added attribute:

    <measure number="6" width="0.00">
      <attributes>
        <measure-style>
          <multiple-rest>4</multiple-rest>
          </measure-style>
        </attributes>
      <note>
        <rest/>
        <duration>4</duration>
        <voice>1</voice>
      </note>
    </measure>

• [ ] TODO: Add Vexflow.MultiMeasureRest to type definitions

Sample:
Multi-Measure-Rest_sample.musicxml.zip

Musescore Rendering:

OSMD 0.7 Rendering:

This will have a few small challenges like needing to skip creating GraphicalMeasures and incrementing measure number count for measureNumberLabel, but the Vexflow part should be easy.

[sschmidTU]

Done.

Added new OSMD Function Test - Multiple Rest Measures to the demo.

[sschmidTU]

I suppose the measure number labels need a change now,
they should be drawn after a multi rest measure if the interval between labels (e.g. every 3 measures) fell into the multi rest measure.

[matt-uib]

@sschmidTU Yes makes sense to adapt the numbering, but is it really such a coincidence, that no numbering falls on a rendered measure?
Actually measure 9 is rendered in your image for example, but no number is shown - seems some other problem here...

[sschmidTU]

Fixed the measure number label generation.
The problem was that it checked for the measure in exactly that interval (e.g. in 2 measures), which can now be inside a multirest.
Now, it checks whether the measure number is greater or equals the previous label plus the interval.

[MilesMorel]

This is awesome! Very nice!!

[sschmidTU]

By the way, you can disable multiple rest measures by setting:

osmd.EngravingRules.RenderMultipleRestMeasures = false;

This will render all rest measures individually.