Main is now targeting .NET 7

This is a heads up that the primary repos of the stack have branched for .NET 6 GA/servicing/RCs, and that the `main` branch for those repos has become .NET 7.

## Anything special to note about .NET 7?

The biggest difference between .NET 6 and .NET 7 flow is that the SDK repos will have their own channel (.NET 7.0.1xx SDK) from the very beginning. While .NET 6 had this channel, we never used it in development. For .NET 7 we will have a runtime and SDK channel from the beginning. Having this split also makes it easier to identify potentially problematic stack dependencies.

## What does this mean for the repos I'm using?

If you're using any of the repos below, then: the `main` branch has been updated to target .NET 7 or .NET 7.0.1xx (for SDK repos).

| Repo | Channel |
| ----------------------------------------------------------------- | ---------------- |
| [dotnet/aspnetcore](https://github.com/dotnet/aspnetcore) | .NET 7 |
| [dotnet/efcore](https://github.com/dotnet/efcore) | .NET 7 |
| [dotnet/emsdk](https://github.com/dotnet/emsdk) | .NET 7 |
| [dotnet/icu](https://github.com/dotnet/icu) | .NET 7 |
| [dotnet/runtime](https://github.com/dotnet/runtime) | .NET 7 |
| [dotnet/windowsdesktop](https://github.com/dotnet/windowsdesktop) | .NET 7 |
| [dotnet/winforms](https://github.com/dotnet/winforms) | .NET 7 |
| [dotnet/wpf](https://github.com/dotnet/wpf) | .NET 7 |
| [mono/linker](https://github.com/mono/linker) | .NET 7 |
| [dotnet/installer](https://github.com/dotnet/installer) | .NET 7.0.1xx SDK |
| [dotnet/roslyn](https://github.com/dotnet/roslyn) | .NET 7.0.1xx SDK |
| [dotnet/sdk](https://github.com/dotnet/sdk) | .NET 7.0.1xx SDK |
| [dotnet/templating](https://github.com/dotnet/templating) | .NET 7.0.1xx SDK |

There are quite a few other repos that were targeting .NET 6 that are not part of the main product flow. Their config might need to be tweaked by the repo owners to do the right thing depending on their development schedules:

* [aspnet/AspLabs](https://github.com/aspnet/AspLabs)
* [dotnet/command-line-api](https://github.com/dotnet/command-line-api)
* [dotnet/format](https://github.com/dotnet/format)
* [dotnet/hotreload-utils](https://github.com/dotnet/hotreload-utils)
* [dotnet/iot](https://github.com/dotnet/iot)
* [dotnet/llvm-project](https://github.com/dotnet/llvm-project)
* [dotnet/msquic](https://github.com/dotnet/msquic)
* [dotnet/runtime-assets](https://github.com/dotnet/runtime-assets)
* [dotnet/scaffolding](https://github.com/dotnet/scaffolding)
* [dotnet/test-templates](https://github.com/dotnet/test-templates)
* [dotnet/wcf](https://github.com/dotnet/wcf)
* [microsoft/vstest](https://github.com/microsoft/vstest)
* [xamarin/xamarin-android](https://github.com/xamarin/xamarin-android)
* [xamarin/xamarin-macios](https://github.com/xamarin/xamarin-macios)

.NET 7 and .NET 6 RC 2 info will be added soon to [dotnet/installer](https://github.com/dotnet/installer).