Use ProjectConfigurationDescription to render inner-build pivots instead of hard coding to TFM

[ladipro]

We should configure using ProjectConfigurationDescription instead, but it's a bit chatty--maybe only the values on the right-hand side?

Originally posted by @rainersigwald in #8619 (comment)

[rainersigwald]

By "right-hand side" I mean that the typical disambiguator from the .NET SDK is something like

TargetFramework=net7.0

Which is a lot of characters and not too interesting. I think the same thing but dropping any TargetFramework= might be good, or we could drop the before-the-equals on every copy of the item to produce strings like net8.0;Value2;Value3 from ProjectConfigurationDescription that has

• TargetFramework=net8.0
• Qualifier2=Value2
• Qualifier3=Value3