Rename LogicalTypeCasts class variables in the castTo method.

    // Old
    private static CastingRuleBuilder castTo(LogicalTypeRoot sourceType) {
        return new CastingRuleBuilder(sourceType);
    }
    // New
    private static CastingRuleBuilder castTo(LogicalTypeRoot targetType) {
        return new CastingRuleBuilder(targetType);
    }