Creates, registers, and initializes the Package for this
model, and for any others upon which it depends. Simple
dependencies are satisfied by calling this method on all
dependent packages before doing anything else. This method drives
initialization for interdependent packages directly, in parallel
with this package, itself.
Of this package and its interdependencies, all packages which
have not yet been registered by their URI values are first created
and registered. The packages are then initialized in two steps:
meta-model objects for all of the packages are created before any
are initialized, since one package's meta-model objects may refer to
those of another.