schema matching: resolve workspace variables in xsdUri

[GitMensch]

I have different workspaces with same named xsd's (different versions) at the same place.
Currently the configuration entries seem to be hard-wired (full local path), it would be useful to be able to use ${workspaceRoot] in this setting.

Example now:

        {
            "xmlns": "http://www.super.web/xsd/SpecialTypes.xsd",
            "xsdUri": "file:////data/projects/project1/external/xsd-files/SpecialTypes.xsd",
            "strict": false
        },

Example with resolving workspaceRoot (there's a workspace folder "xsd" mapped to the path above):

        {
            "xmlns": "http://www.super.web/xsd/SpecialTypes.xsd",
            "xsdUri": "file://${workspaceRoot:xsd}/SpecialTypes.xsd",
            "strict": false
        },

See vscode variables reference.