Validate v8 build with .NET 8

[martincostello]

Add a build configuration to validate in CI that Polly v8 works as expected with .NET 8 with a net8.0 TFM using the prerelease packages.

Once preview 4 is available, remove the internal TimeProvider copy and use the version shipping in a NuGet package instead.

Once .NET 8 ships as stable in November, we can then roll net8.0 into the main build setup and ship a package that explicitly supports it.

[martintmk]

As a part of this task we should also unify all Microsoft.Extensions.* and System.* packages to version 8.0.0. These versions should fix known compatibility problems seen in versions. Would simplify our setup too as we don't have to deal with different versions for each framework anymore.

[martincostello]

Yep I'll sort that out once it's available (that's p4 too right?). For now I've just extended the multi-targeting while I'm playing with it locally.

[martintmk]

that's p4 too right?

Hopefully yes, we just need to wait until the System.Bcl.TimeProvider package appears in nuget :)

[martintmk]

@martincostello I came across this post:

https://devblogs.microsoft.com/dotnet/package-validation/

I think it's something we can do for V8 too! ;)

[martincostello]

Yep it would be good to add that too - I already use it in a number of my OSS projects. We should be able to enable it separate from the .NET 8 upgrade.

[martincostello]

Added package validation in #1172. There's also some additional checking already as part of #1134.

[github-actions]

This issue is stale because it has been open for 60 days with no activity. It will be automatically closed in 14 days if no further updates are made.

[martincostello]

Completed by #1144.