Add TopDownMutatorContext.CreateModule

Allow a module to create other modules as if they were specified
in a blueprint file.  CreateModule takes the name of a module type,
calls the factory function the module type, and then inserts
properties into the property structs returned by the factory.

Bug: 64161749
Test: TestCreateModule
Change-Id: Ic1903305d6b08eae1edc7f0fb4137e85544aac0f