[Infra] - Expose SuperEditor and SuperReader test builders

[matthew-carroll]

When testing SuperEditor and SuperReader, we regularly use associated builders, which conveniently organize the pumped widget tree, as well as all of the configurations for the SuperEditor or SuperReader widget.

Uses of this package should have access to those tools, too.

Audit the existing tools for appropriate naming and documentation, then move those tools into the public API for the package.