Microsoft.AspNetCore.Http.Features split, no longer shipped as a package

## Microsoft.AspNetCore.Http.Features split, no longer shipped as a package

Microsoft.AspNetCore.Http.Features is being split into two assemblies, Microsoft.AspNetCore.Http.Features and Microsoft.Extensions.Features.

### Version introduced

6.0

### Old behavior

Microsoft.AspNetCore.Http.Features 5.0 shipped both in the ASP.NET shared framework and as a nuget package.

Microsoft.AspNetCore.Http.Features 5.0 targeted .NET 4.6.1, .NET Standard 2.0, and .NET 5.0

### New behavior

Microsoft.AspNetCore.Http.Features 6.0 will ship only in the ASP.NET shared framework, not as a nuget package.

Microsoft.AspNetCore.Http.Features 6.0 will target .NET 6.0 only.

Microsoft.Extensions.Features 6.0 will ship both in the ASP.NET shared framework and as a nuget package.

Microsoft.Extensions.Features 6.0 will target .NET 4.6.1, .NET Standard 2.0, and .NET 6.0

The following types will move to the new assembly. The namespaces will not be changed and type forwards will be added for compatibility.

```
namespace Microsoft.AspNetCore.Http.Features
IFeatureCollection
FeatureCollection
FeatureReference<T>
FeatureReferences<T>
```

### Reason for change

This allows these core types to be shared more broadly across components, while also allowing the remaining Http specific components in Microsoft.AspNetCore.Http.Features to take advantage of new runtime and language features.

### Recommended action

When upgrading to ASP.NET 6.0 remove any packages references for `Microsoft.AspNetCore.Http.Features`. Add a package reference for `Microsoft.Extensions.Features` only if required.

Class libraries that need to consume the types from `Microsoft.AspNetCore.Http.Features` should add a FrameworkReference instead:

```
  <ItemGroup>
    <FrameworkReference Include="Microsoft.AspNetCore.App" />
  </ItemGroup>
```

https://docs.microsoft.com/aspnet/core/fundamentals/target-aspnetcore?#use-the-aspnet-core-shared-framework

Libraries with out of date references may encounter a `TypeLoadException` or the following error:
```
Error	CS0433	The type 'IFeatureCollection' exists in both 'Microsoft.AspNetCore.Http.Features, Version=5.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60' and 'Microsoft.Extensions.Features, Version=6.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60'
```

This can be mitigated by adding the FrameworkReference shown above to any of the affected projects.

See https://github.com/dotnet/aspnetcore/issues/32307 for questions.

### Category

ASP.NET

### Affected APIs

[IFeatureCollection](https://docs.microsoft.com/dotnet/api/microsoft.aspnetcore.http.features.ifeaturecollection)
[FeatureCollection](https://docs.microsoft.com/dotnet/api/microsoft.aspnetcore.http.features.featurecollection)
[FeatureReference](https://docs.microsoft.com/dotnet/api/microsoft.aspnetcore.http.features.featurereference-1)
[FeatureReferences](https://docs.microsoft.com/dotnet/api/microsoft.aspnetcore.http.features.featurereferences-1)
  


---
#### Issue metadata

* Issue type: breaking-change

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Microsoft.AspNetCore.Http.Features split, no longer shipped as a package #462