MusicXML track volume and balance not importing

[jordanske]

Your environment

• Version used: 1.2.0-alpha.64
• Platform used: JavaScript
• Rendering engine used: SVG
• Browser Name and Version: Any
• Operating System and version: Any
• Link to your project: ~

In follow up of #445, track volume and balance are also not imported from MusicXML format.

Expected Results

Initial track volume and balance like configured in MusicXML.

Observed Results

All track volumes and balances have the default values.

Steps to Reproduce (for bugs)

1. Load any .musicxml file with non default track volume and balance
   For example: Track Volume and Balance Test.zip

Possible Solution

Fix the MusicXmlImporter to import these values.

I can work on a pull requests this weekend.

[Danielku15]

Looking forward to your contribution. Here some implementation hints:

alphaTab/src/importer/MusicXmlImporter.ts

Line 1389 in 72512ce

private parseMidiInstrument(element: XmlNode, track: Track): void {

https://usermanuals.musicxml.com/MusicXML/Content/CT-MusicXML-midi-instrument.htm

[Danielku15]

Closed with #454