[java] UnusedModifier doesn't check static keyword on nested enum declaration

[jsotuyod]

Rule Set: unused/UnusedModifier

Description:
Enums are static by default. Explicitly setting them matches this rule's criteria:

For historical reasons, modifiers which are implied by the context are accepted by the compiler, but are superfluous.

Code Sample demonstrating the issue:

public @interface Test {
  public static enum EnumSample {
    TEST;
  }
}

PMD will find no violations on this annotation, 1 violation is expected.

The behavior is consistent when nested in classes, annotations and interfaces.

Running PMD through: Any