Discovery mechanism for customizing metaclasses with a script using ExpandoMetaClass

Currently, it is possible to define custom MetaClasses at load time by following the convention:

groovy.runtime.metaclass.java.lang.StringMetaClass

Creating this StringMetaClass in this specific place will use this metaclass in lieu of the default metaclass.

By adding ExpandoMetaClass back in Groovy, we should provide a mechanism for customizing metaclasses.
For instance, we could create an expandoMetaClassScript.groovy in the package groovy.runtim.metaclass.
And in this script, we would use ExpandoMetaClasses to customize classes behaviour further.