Uniform attribute level refactoring types

[jodavimehran]

There are some attribute level refactoring-types like ChangeAttributeTypeRefactoring, RenameAttributeRefactoring, MergeAttributeRefactoring, and SplitAttributeRefactoring has instances of VariableDeclaration class as attributes to keep the state of a refactored attribute before and after refactoring.
However, the other attribute level refactoring types like MoveAttributeRefactoring and AddAttributeAnnotationRefactoring have instances of UMLAttribute class to do the same.

Therefore, to make the code more uniform, it is better to refactor those refactoring classes to use UMLAttribute, which contains more information in comparison to VariableDeclaration.

[tsantalis]

This change has many implications that you did not consider.
The UMLAttribute.toString() is different than the VariableDeclaration.toString(), which affects the refactoring descriptions generated by toString(). This will make the test calculating the precision and recall to fail in matching some cases in the oracle.
Also equals() and hashCode() have a different behaviour, because VariableDeclaration takes into account the VariableScope, while UMLAttribute does not take into account the VariableScope.
The toString(), equals() and hashCode() in all 4 refactorings should be updated to be consistent with the previous implementation.

[tsantalis]

@jodavimehran Thanks for updating toString(), equals() and hashCode()
Could you please do the same for leftSide() and rightSide() in all 4 refactorings?
Replace attribute with attribute.getVariableDeclaration()