So this is RFC-ish. I've been struggling naming the idea of
creating a dagster type where all you want to do is an instance of
check. Here I'm proposing that we just use the class
PythonObjectDagsterType and eliminate the define_python_object_type.
This will make it clear that it much more similar to the DagsterType
and doesn't involve any sort of global registry
Depends on D1906