Export the ErrorCode enum in the type declaration file

[nschirmer]

Description

Exported the ErrorCode enum so that consumers can match specific errors against Snowflake.ErrorCode.ERR_CONN_CONNECT_STATUS_CONNECTING for example.

Checklist

• Format code according to the existing code style (run npm run lint:check -- CHANGED_FILES and fix problems in changed code)
• Create tests which fail without the change (if possible)
• Make all tests (unit and integration) pass (npm run test:unit and npm run test:integration)
• Extend the README / documentation and ensure is properly displayed (if necessary)
• Provide JIRA issue id (if possible) or GitHub issue id in commit message

[github-actions]

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[nschirmer]

I have read the CLA Document and I hereby sign the CLA