Rework BindingRuntimeTypes

BindingRuntimeTypes serves to bring together GeneratedTypes and
SchemaNodes. We do this in a a number of different ways, but a lot of
the times this ends up looking a Type and then finding the SchemaNode
which generated it -- and then perhaps inquire children by SchemaNode
(which again is looked up in some way).

Once we have done these cross-lookups, we resolve the Type to a Class
through BindingRuntimeContext and instantiate a
DataContainerCodecPrototype, which holds these (and other) bits
together.

Current code relies on DerivableSchemaNode and SchemaNode-based lookups
to resolve these due to historical reasons. Our Generator infrastructure
already has AbstractExplicitGenerator.getOriginal() to perform the
equivalent operation.

This patch defines a RuntimeType base interface which holds together an
EffectiveStatement and a Generated type. We also define a
RuntimeTypeContainer to expose lookup methods for inquiring child
RuntimeTypes as appropriate.

BindingRuntimeTypes serves as the root of a tree hierarchy, where
RuntimeType is a leaf node and CompositeRuntimeType is an interior
node.

NodeCodecContext and its subclasses are modified to maintain a reference
to their backing RuntimeType and issue appropriate localized lookups.

JIRA: MDSAL-696
Change-Id: I45850d320e01fce0b227512b9f5f7b19331df60e
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>