QVT14 — QVTr - Fixed-point semantics

Issue 18572 highlighted that QVT 1.1 seemed to require inconsistent fixed-point semantics. The resolution solved the inconsistency by requiring repeated execution to be external to QVT.

However some transformations such as the TTC PetriNet to StateChart require repeated transforming.

If QVTr supported the TypedModel::uses property then an endogeneous transformation whose input TypedModel uses its output TypedModel makes the repeated execution for fixed-point semantics consistent.

Need to update 7.7/add a fixed-point semantics section.

Need to add TypedModel::uses to the QVTr concrete syntax.