[java] LocalVariableCouldBeFinal shouldn't report unused variables

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Affects PMD Version: 6.x

Rule: LocalVariableCouldBeFinal

Description:

A local variable, that is just defined but not used, is a different problem: UnusedLocalVariable. Make the variable final doesn't fix anything.

Found via #3123. It's already fixed with PMD 7.0.0-rc1.
Was fixed via #3113.

Code Sample demonstrating the issue:

public class Foo {
    public void test1() {
        int a = 0; // not final, but also not used
    }
}

Expected outcome:

PMD reports a violation at line 3, but that's wrong. That's a false positive.