HttpRequestData should preserve the capitalization of custom http header keys

Hi all!

I have a function running .NET 5 in an isolated process. When the HTTP trigger is hit with a request containing some custom http header key (ie. My-SPECIAL-CaSe-sensitive-Header), the capitalization seems to be lost when accessing the header via `HttpRequestData`. The `BindingContext`, however, holds the custom header key with the original capitalization. `HttpRequestData `should also preserve the original capitalization of custom http headers keys.



Thank you!
David

Start by locating the HttpRequestData and BindingContext handling for HTTP trigger headers, then reproduce the issue with a custom header such as My-SPECIAL-CaSe-sensitive-Header. Compare the capitalization exposed by both objects; done means HttpRequestData preserves the original capitalization of custom header keys.

Written by the indexing model from the issue text.