mergeWith method
Implementation
DartDefine mergeWith(DartDefine define) {
final merged = <String, String>{};
final mergedFiles = <String>[];
merged.addAll(define._defined);
mergedFiles.addAll(define._files);
merged.addAll(_defined);
mergedFiles.addAll(_files);
return DartDefine(defined: merged, files: mergedFiles);
}