Move grouping/instantiation lookup code

Move grouping/instantiation lookup code

DatObjectCodecContext should not be concerned with relationships
between parent and child, certainly not to the point of dealing with
where an original grouping leaf is instantiated.

The natural place for this logic is BindingRuntimeContext or
BindingRuntimeTypes, as those get their indices from
mdsal-binding-generator -- which is the core component understanding
these relationships.

Also ditch use of Optionals for tracking walk through dependencies,
which clears up some ugly casts.

Change-Id: I72bfa499794b55c0c6266462b36df56c2ac085c2
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>