Improved the MSBuild selection logic. The standalone instance inside OmniSharp is now preferred over VS2017, with VS2019 given the highest priority. This ensures that .NET Core 3.0 works correctly. It is also possible manually provide an MSBuild path using OmniSharp configuration, which is then always selected. (omnisharp-roslyn#1541, PR: omnisharp-roslyn#1545)

    {
        "MSBuild": {
            "MSBuildOverride": {
                "MSBuildPath": "C:\\Program Files (x86)\\Microsoft Visual Studio\\2017\\Enterprise\\MSBuild\\15.0\\Bin",
                "Name": "vs2017 msbuild"
            }
        }
    }