refactor: remove CtParameterReferenceImpl#declaringExecutable

[monperrus]

By analyzing #1869, I realize that CtParameterReference and CtParameterReferenceImpl are badly designed. The problem is that CtParameterReference is stateful with a superfluous pointer to an executable reference:

• this goes against the design of philosophy of Spoon references that are mean to be resolved dynamically (instead of hard-wired links)
• when a parameter reference is moved in a transformation (eg from one variable to another), the result of getDeclaration(), done with dynamic lookup, can become inconsistent with the result of getDeclaringExecutable()
• when a parameter reference is cloned, the result of getDeclaration(), done with dynamic lookup is correct (see CtExecutableReference in cloned method should refer to the clone, not to the method being cloned. #1869 (comment)), yet inconsistent with the result of getDeclaringExecutable(), which is not changed during cloning. This is one facet of the problem discussed in CtExecutableReference in cloned method should refer to the clone, not to the method being cloned. #1869.

The solution presented here it to remove the get/setDeclaringExecutable from interface CtParameterReference, and to remove the corresponding state in the implementation (field declaringExecutable).

This fixes the three problems described above. There are a few test changes, which are minor, they were simply directly unit-testing get/setDeclaringExecutable.

Once this one is merged, there will be other PRs for #1869.

[pvojtechovsky]

I agree that field CtParameterReferenceImpl#executable should be removed.

But would it be possible to KEEP CtParameterReference[Impl]#getDeclaringExecutable() ?? May be we can mark it @derived and compute it's value from the Spoon model?

[monperrus]

you're right. it's better for backward compatibility. done.

[pvojtechovsky]

Looks good to me. @monperrus are you done with this PR? Do you want to merge it soon (tomorrow morning) or should we wait for feedback of others here?

[spoon-bot]

API changes: 1 (Detected by Revapi)

Old API: fr.inria.gforge.spoon:spoon-core:jar:6.2.0-20180221.155557-103 / New API: fr.inria.gforge.spoon:spoon-core:jar:6.2.0-SNAPSHOT

	Method was removed.
Old	method CtParameterReference#setDeclaringExecutable(CtExecutableReference)
New	none
Breaking	binary: breaking

[monperrus]

OK to merge.