Move terminal test to properties

[som-snytt]

Follow up #10751 to be more like #10752

ShellConfig has a comment that the same property for colorization is used by TypeDebugging.

Notify the Scala Store to restock the "be more like Seth" t-shirts.

[som-snytt]

Not what we normally mean by "test-driven development".

Mima complains about the new method. It is private[scala] and used only from Properties and also from ShellConfig (which must be run with its library version).

I don't like that Properties is performing the console probe, for a property that is used by compiler and repl.