Investigate different methods of generating simple names for anonymous entities

When processing an anonymous entity (such as an anonymous class), Spoon seems to rely on the following code:
```java
// ... other code
if ((type instanceof CtClass || type instanceof CtInterface)
&& typeDeclaration.binding != null
&& (typeDeclaration.binding.isAnonymousType() || typeDeclaration.binding instanceof LocalTypeBinding && typeDeclaration.binding.enclosingMethod() != null)) {
type.setSimpleName(computeAnonymousName(typeDeclaration.binding.constantPoolName()));
}
// ... other code
```

(present [here](https://github.com/INRIA/spoon/blob/master/src/main/java/spoon/support/compiler/jdt/JDTTreeBuilderHelper.java#L856))

This results in a **numeric "simple name"** being generated and given to the anonymous entity (implementation [here](https://github.com/INRIA/spoon/blob/master/src/main/java/spoon/support/compiler/jdt/JDTTreeBuilderHelper.java#L104) but is also present in snippet below).
```java
static String computeAnonymousName(char[] anonymousQualifiedName) {
final String poolName = CharOperation.charToString(anonymousQualifiedName);
return poolName.substring(poolName.lastIndexOf(CtType.INNERTTYPE_SEPARATOR) + 1);
}

```

This could result in some issues when we'd like to have simple names that are more _representative_ of the anonymous entities. For instance, using just numeric names for anonymous entities seems to have caused the following issue: https://github.com/SpoonLabs/gumtree-spoon-ast-diff/issues/347 (see the discussion for more).

We can probably improve this anonymous naming convention. One idea could be to use the parent/super-class in generating the simple-name, among others.