Support net8 SDK in dotnet-svcutil

[betmix-matt]

Resolves Issue #5362

[betmix-matt]

If we can get this merged before the 2.2 release, it can include both .NET 7 and .NET 8 support for dotnet-svcutil

[imcarolwang]

Looks good to me.

[0xced]

I think the dotnet-svcutil tool should be configured to roll forward to the latest major .NET version, just like the dotnet ef tool did.

Basically, that means adding the <RollForward>Major</RollForward> property in the project file.

So that when new runtimes are released the tool will automatically work with the new runtime. There's even a proposal for this behavior to be the default for .NET tools (dotnet/sdk#30336) but it has not been implemented yet.