Support arrays in query/path/header

[ejball]

We should probably try to support some/all of what OpenAPI supports. But it's hard for me to get excited about adding that level of complexity to all code generators. Even "simple" CSV gets complicated when deciding how to encode a comma.

[ejball]

The syntax is supported by Facility, so we should support it if we can.

We will probably need to add "raw" alternatives to HttpMethodMapping:

public Func<TRequest, IReadOnlyDictionary<string, IReadOnlyList<string>>> GetRawUriParameters { get; set; }

We should write helper functions instead of generating all of the code inline.

We will need to maintain backward compatibility but we can ignore the non-raw if the raw is specified.