Drop .Net Core 2.1 support

[azchohfi]

Describe the bug

We should drop support for netcoreapp2.1. It is out of life, and our tests will start to fail on ADO since we don't manually install this framework.

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[Sergio0694]

This was on my ToDo list as well and likely the first thing I wanted to do in the .NCT 😄
Are the .NET Core 2.1 tests only in the .NET unit tests, or do those affect the UWP/WinUI projects too?
If it's the former I can just take this after the split, otherwise happy to help with this with a PR for this repo if you're busy 😊

[azchohfi]

This affects the HighPerformance package, as well as the Notifications one.
I'm mostly worried about the notifications, as we support older targets and need to keep them working:
https://github.com/CommunityToolkit/WindowsCommunityToolkit/blob/main/Microsoft.Toolkit.Uwp.Notifications/Microsoft.Toolkit.Uwp.Notifications.csproj#L4
I believe we only need to update to 3.1 and we should be good to go, but its better to keep this until 8.x (breaking change).
Btw, I do not have the bandwidth to work on this, sorry.

[Sergio0694]

No worries! So if we're both busy right now and you think stripping .NET Core 2.1 from the Notifications package might be a bit tricky, here's an idea: we don't do anything for now, we wait for the .NET Community Toolkit split first, and then we'll each strip .NET Core 2.1 in our respective Toolkits when we have time. The .NCT stuff going away will mean you'll only have to deal with the single Notifications package when you have time to look into that (I'm also not familiar with that project myself), and I'll take care of removing .NET Core 2.1 from the .NET unit tests projects instead once the new repo is live. How does this sound? 🙂

[azchohfi]

Sounds great!
Is there a ball park date for when do you think the NCT bits will be moved?

[Sergio0694]

Awesome! We should do that right after 7.1.1 is out, probably so sometime late next week or the week after that? 😄

[Sergio0694]

@azchohfi I removed all .NET Core 2.1 targets from the .NET Community Toolkit (CommunityToolkit/dotnet@9410983), and the entire repo has been migrated and setup now. Let me know if you need help with a PR to delete everything related to the .NCT. Then the only remaining place to remove .NET Core 2.1 from should just be that notification project we talked about 😊