Closure improvements

[brachy84]

• Adds a mixin to Closure so which delegates the call method to GroovySandbox so we never have to worry about forgetting that.
• Adds helper methods in ClosureHelper to add a variable holder an to get the under lying closure from a functional interface object.
• cleans up some other code

Example:
Add this to Crafting (oor anywhere else)

public void test(BooleanSupplier supplier) {
        Closure<?> closure = ClosureHelper.getUnderlyingClosure(supplier);
        ClosureHelper.withEnvironment(closure, new TestEnv(), true);
        GroovyLog.get().info("Supplier: {}", supplier.getAsBoolean());
}

Add TestEnv class

private static class TestEnv {

        public final String testVar = "environment variable";

        public void testFunc() {
            GroovyLog.get().info("environment method");
        }
}

In a script add

crafting.test {

    log.info(testVar)
    testFunc()

    return true
}