(feature, csharp): Add support for allow-multiple query params

[amckinney]

This adds support for allow-multiple query parameters, which are serialized in explode format (e.g. &foo=one&foo=two).

The change takes place in two files:

• The RawClient.cs core utility now supports IEnumerable collection types in the BuildUrl helper.
  • The string type requires special handling since it is the only primitive that implements the IEnumerable interface.
• The query parameters are attached to the _query parameter with simple LINQ expressions like the following:

var _query = new Dictionary<string, object>() { };
_query["operand"] = request
    .Operand.Select(_value => JsonSerializer.Serialize(_value))
    .ToList();

There's still some missing functionality here. As it stands, we don't support deepObject query parameters, so we'll likely need to revisit the BuildUrl implementation.

[dcb6]

nice! 🚀