Allow iteration over all dependencies in a check

[effad]

Consider the case where a check is programmatically built out of a set of objects, e.g.

Check check = validator.createCheck()
	.withMethod(this::atLeastOneParameter);
for (ComboFormField<?> combo : combos.values()) {
	check
		.dependsOn(combo.getDataIndex(), combo.chosenItemProperty())
		.decorates(combo.getPresentation())
	;
}
check.immediate()

Now in the check-Method we must iterate over all the given properties to check if at least one value was given, but there is no way to do that easily:

private void atLeastOneParameter(Check.Context check) {
	// TODO :: iterate over all dependencies
}

We must iterate over combos again and pick the same property, which violates the DRY principle and inserts an ugly dependency between the two places in the code.