* Add native stacktrace on iOS
* Add native stacktrace on Android
* format and changing naming to errorWithCode on iOS
* reformat
* Remove stacktrace from decodeEnvelope, not needed.
* Separate encodeErrorEnvelopeWithStacktrace with original encode function
* Add unit tests
* re-format
* change comments for stacktrace
* Remove changes for iOS
Co-authored-by: Ben Li <libe@google.com>