Make Kestrels Internals truly internal.

[jkotalik]

Fixes #8306. Big change here so I'll give you the rundown.

Big Picture:

• Removes all .Internal namespaces and moves appropriate methods to internal
• Makes all types in Microsoft.AspNetCore.Server.Kestrel.Transport.Abstractions public. These types are already exposed on public API
• Makes KestrelServerOptionsSetup public

Nitty Gritty:

• Any method that had a pubternal API was either changed to internal or public accordingly
• Tests that took in enums that were changed from public to internal were changed appropriately.

For any public API, we probably need to add xml comments appropriately.

[jkotalik]

We should also probably have an API review for these changes if we decide to many anything truly public.

@sebastienros let's also make sure this doesn't break the platformbenchmark scenario.

[pranavkm]

Code changes look great. I'd get sign off from someone more familiar with the API being made public

[sebastienros]

I don't know exactly what will be broken, but chances are that this will break it. Here is a list of internal namespace usages:

https://github.com/aspnet/AspNetCore/blob/master/src/Servers/Kestrel/perf/PlatformBenchmarks/Program.cs#L7

https://github.com/aspnet/AspNetCore/blob/master/src/Servers/Kestrel/perf/PlatformBenchmarks/IHttpConnection.cs#L6

https://github.com/aspnet/AspNetCore/blob/master/src/Servers/Kestrel/perf/PlatformBenchmarks/BenchmarkApplication.cs#L7

https://github.com/aspnet/AspNetCore/blob/master/src/Servers/Kestrel/perf/PlatformBenchmarks/BenchmarkApplication.HttpConnection.cs#L9

https://github.com/aspnet/AspNetCore/blob/master/src/Servers/Kestrel/perf/PlatformBenchmarks/AsciiString.cs#L6

I would suggest to also change PlatformBenchmarks at the same time such that it will work with this PR, or adapt the bits that are used to make them public. Ideally some parts of PlaintextBenchmarks should be in Kestrel and directly reusable in the app.

[sebastienros]

Looking at your changes I assume it's actually a good change for the PlatformBenchmarks as some use types will now become really public. Still good if some of the things in PB were in Kestrel directly.

[halter73]

YESSSS! Overall, I'm super happy about this change.

[davidfowl]

This is going to make it impossible to write a kestrel transport right?

[halter73]

This is going to make it impossible to write a kestrel transport right?

The plan is to leave the transport abstractions and a few other things like connection adapters pubternal in this first pass.

[jkotalik]

Updated with feedback. I think this is looking muchhhhh better.

[halter73]

I wish git better tools around normalizing BOMs similar to what it has for line endings gitattributes.