Split Http.Features assembly

[pranavkm]

• Create new project Microsoft.Extensions.Features (netstandard2.0)
• Move IFeatureCollection, FeatureCollection etc to this assembly. Add type-forwarding from Http.Features -> IFeatureCollection.
• SignalR will reference this new project. This is a breaking change for SignalR clients but it's ok since this is already broken
• Update Microsoft.AspNetCore.Http.Features to target net6.0 and stop publishing it as a NuGet package.

Thanks for contacting us.
We're moving this issue to the Next sprint planning milestone for future evaluation / consideration. Because it's not immediately obvious that this is a bug in our framework, we would like to keep this around to collect more feedback, which can later help us determine the impact of it. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

[Tratcher]

Followup for Http.Features:

• Stop shipping as a nuget package
• Target only the latest TFM

[davidfowl]

I think we should attempt this in preview5

[Tratcher]

The changes are merged but I'm keeping this issue open until:

• I can test the results from a real build, especially regarding the shared framework.
• The announcement is posted.

[Tratcher]

I've confirmed this works as expected in the 6.0.100-preview.5.21230.5 SDK build.

Console App net6.0

• Project reference to library1 net5.0
  • Package reference to Microsoft.AspNetCore.Http.Features 5.0.0
• Project reference to library2 net6.0
  • Package reference to Microsoft.Extensions.Features 6.0.0-preview.5.21229.9

I got the same result when I converted the libraries to packages.

Compile time 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'

Mitigation: Add the following to any one of the three projects and it will correctly unify everything.
<FrameworkReference Include="Microsoft.AspNetCore.App" />

[Tratcher]

aspnet/Announcements#462