* Use assets.json as single source of truth for OpenRCT2 assets
This ensures there's single source of truth for all downloadable assets.
I figured the "version" information is actually redundant because we can
embed the whole URL as the "zipversion", therefore this is dropped now.
The newly-introdcued MSBuild task uses Roslyn-based code and I updated
`DownloadDependency` task to RoslynCodeTaskFactory as well.
* Rename OpenMSX to OpenMusic