Buffer input stream for System.Web adapters

[twsouthwick]

This sets up the input stream to be buffered and reads it all into memory to mimic the behavior of System.Web. This can be turned on per endpoint via the SystemWebAdapterAttribute metadata entry.

A WebApi endpoint has also been added to test similar behavior between the two frameworks that can be expanded as more features are brought online.

[twsouthwick]

@davidfowl @Tratcher I haven't done much with endpoint metadata, but this looks like a good way to allow configurability per endpoint for System.Web compatibility. I'm assuming "last one wins" is a decent enough way to manage it and I don't need to deal with merging multiple layers of metadata (i.e. through the GetOrderedMetadata<> call).

As always, feedback is appreciated!

[twsouthwick]

@Tratcher I had to put back the services.AddSingleton<PreBufferRequestStreamMiddleware>(). Without that, I get an error about it not being registered. Maybe there's a different pattern you're thinking of?

[Tratcher]

@Tratcher I had to put back the services.AddSingleton<PreBufferRequestStreamMiddleware>(). Without that, I get an error about it not being registered. Maybe there's a different pattern you're thinking of?

That might be because you're using IMiddleware, we don't usually use that. Here's the more common pattern:
https://github.com/dotnet/aspnetcore/blob/5fa80eb167ac3ae2c03590b135379fc3e3621175/src/Middleware/Diagnostics/src/DeveloperExceptionPage/DeveloperExceptionPageMiddleware.cs#L43-L86