AST Simplified toString

[rcosta358]

This PR replaces the toString() methods from the AST classes with the toSimplifiedString() methods. This way, the error messages don't include the fully qualified names for ghosts, which improves their readability by reducing their verbosity.

Example

Before

Refinement Error: #index_7 == 1 && java.util.ArrayList.size(#list_8) == java.util.ArrayList.size(#list_4) + 1 && java.util.ArrayList.size(#list_4) == 0 is not a subtype of 0 <= #index_7 && #index_7 < com.arraylist.ArrayListRefinements.size(#list_8)

After

Refinement Error: #index_7 == 1 && size(#list_8) == size(#list_4) + 1 && size(#list_4) == 0 is not a subtype of 0 <= #index_7 && #index_7 < size(#list_8)

[CatarinaGamboa]

nice refactoring! But what if we have two ghosts from different classes like ArrayList.size and Stack.size? would there be a way to only show the full name if theere are more than 1?

[rcosta358]

I think so, but in that case we need both methods, toString and toSimplifiedString and then choose which one to call.

[rcosta358]

I'll try to do that in another PR and leave this one open.

[rcosta358]

This seems to be a bit harder than I originally thought, so I'll do that in a follow-up PR in the future.