Allow C# records to be used as metadata views

[kzu]

Currently, if you try to use a record type as a metadata view, you get the following error:

System.NotSupportedException: 'The type [TYPE] is an unsupported type of metadata view.'

Given how convenient and concise they are, it would be quite handy if the export provider
supported record types as metadata views. It would just need to invoke the constructor
and any init properties as needed.

[AArnott]

I can't think of a reason why this wouldn't be technically possible. There may be one, but it's a fine idea to pursue. This doesn't seem to unblock any critical scenario though, so as a low priority item, it won't likely get attention from the VS team. If you're interested in submitting a PR, I'd be willing to review and merge it, if it came with adequate automated tests.