RSA-RTE: Enable writing transformation extension also taking prerequisite transforms into account

Problem description
When opening a source file after transformation, the indexer throws
lots of errors and warnings because of unresolved items.
(There are actually several related issues regarding the CDT project
properties, but thats out of scope here.)
One major cause were the include directories, which we now set in the
transformation configuration.
One other issue were the compiler symbols, which are set in the
transformation configuration, but they arent set
in the project properties correctly, therefore I have created an
transformation extension plugin. (See attachments)

However when developing on it I ran into the following:
With a rule extending com.ibm.xtools.umldt.rt.transform.cpp.
UML2CppTransform the rule is executed for the current transformation
(which is correct.)
However the rule is not executed for prerequisite transformations which
also include the extension.
(Running a prerequisite transformation separately, does work, so I don
t think there is a problem with the extension.)

An option would be to extend: com.ibm.xtools.umldt.rt.transform.cpp.
NodeTransform but then the context is still the parent context,
while the source is com.ibm.xtools.umldt.rt.transform.internal.model.
TransformGraph$Node which is internal and therefore cant be used.
The target is: com.ibm.xtools.cpp2.model.impl.CPPProjectImpl for
which I cant find any documentation.

I think having the correct transformation context (instead of the
parent context) and corresponding CDT project as targetContainer would
be far more usable. (Anything is better than internal classes)

I guess this is an error on IBMs behalf, but it is possible that I am
doing something wrong.
For now, I traverse the prerequisites myself at the end of the
UML2CppTransform, but there must be a better way.

After discussion on the related PMR. it turned out dat IBM discourages writing Transformation extensions. So we asked to make that possible.

Attached: the transformation extension we currently use.