next: gt_substitute_compiletime_symbols() calls ConstantPropagation

[philip-paul-mueller]

gt_simplify() was explicitly designed such that ConstantPropagation is not called.
This is the main reason why ADR18 explicitly forbids to calls the native dace simplification pipeline.
However, gt_substitute_compiletime_symbols() does calls it, for various reasons, but the implementation is not optimal, because some cases are not handled at all and there is some other strange behaviour.

It also called problems during an update of DaCe.
So we should rework this function to avoid the need to call ConstantPropagation.