Named Request Support

[bleaphar]

This PR introduces named request support to dotnet interactive. It will allow the kernel to maintain named requests so that users are able to use the properties from its request and response in future requests.

Breakdown

• HttpNamedRequest -> This is the structure of a named request with the ability to resolve a path that the user is navigating to
• HttpRequestParser -> This file has been modified to support the parsing of the requests in HttpComments
• HttpCommentRequestNode -> This file represents a named request signifier in an HttpCommentNode, it also has child nodes for the name node which should be @name and the value node which is the actual name of the named request
• HttpRootSyntaxNode -> Has been edited to support binding from the kernel. This was to ensure that declared variables can be resolved with the results of a named request which previously would not have been feasible.
• HttpDiagnostics -> Has been updated to reflect the diagnostic messages associated with the named request
• Tests -> HttpKernelTests for the parsing and using of a named request (incomplete), ParserTests.NamedRequests reflects the parsing of different named request scenarios, ParserTest s.Variables was updated to support the tuple structure that TryGetDeclaredVariables was updated to

[jonsequitur]

The combinatorial tests should probably be updated to include this new syntax.

If you'd like to find some time to pair on it, let me know.