Add debug output to HttpContext and friends

[Tratcher]

Contributes to #48205

I've added debug views to HttpContext and related types. While some of the views appear to be pass through, they actually work to hide internal implementation details from the underlying types. Note we can't put debug views on interfaces so I had to do it directly on implementing types. IIS and HttpSys share a header collection implementation.

The ToString implementations are optional, we could make those private string CreateDebugView() instead.

Other properties to consider:

• Features/FeatureCollection

[JamesNK]

HttpContext.User isn't that useful. An issue to embiggen its debug capabilities: dotnet/runtime#86421

[JamesNK]

Something we should consider is the formatting of properties and values. Existing debugger display attributes tend to use the format IsCancellationRequested = true and Count = 10 while we do IsCancellationRequested: true, which is the format we tend to use in our logging messages.

Idea: We stick with our format Name: value for logs and endpoint metadata and use the equals format Name = value for debugger display. What do you think @Tratcher?

[Tratcher]

Something we should consider is the formatting of properties and values. Existing debugger display attributes tend to use the format IsCancellationRequested = true and Count = 10 while we do IsCancellationRequested: true, which is the format we tend to use in our logging messages.

Idea: We stick with our format Name: value for logs and endpoint metadata and use the equals format Name = value for debugger display. What do you think @Tratcher?

I switched to using = and it seems fine. The one place it's a little odd is when I'm only naming some paramters for brevity:
HttpContext: POST /path application/json StatusCode = 200 application/json
Request: HTTP/2 POST https://Host:port/pathBase/path?q1=1&q2=2 application/json Length = 10
Response: StatusCode = 200, HasStarted = False, Length = (null) application/json
Connection: Id = ConId, Remote = [::1]:12345, Local = [::1]:443, ClientCertificate = (null)

I want things to easily fit into the debug window, and most of these fields seem obvious from context. The expanded view breaks down the individual fields.