Error reporting improvements

[adams85]

Describe the purpose of your pull request

Define error codes (EvaluationErrorCode, RefreshErrorCode) and expose them to the user (EvaluationDetails.errorCode, RefreshResult.errorCode) so they can reliably identify the error type without resorting to guess it by checking the error message (see also: open-feature/dotnet-sdk-contrib#119 (comment))

Also,

• fixes a minor bug in setting type mismatch check (type mismatch should also be reported for allowed flag override values),
• fixes a minor bug in formatting errors (some JS runtimes doesn't include the error message in the stack trace),
• fixes a minor bug in FetchError (name property should be set to the class name).

Related issues (only if applicable)

https://trello.com/c/mU63054x

Requirement checklist (only if applicable)

• I have covered the applied changes with automated tests.
• I have executed the full automated test set against my changes.
• I have validated my changes against all supported platform versions.
• I have read and accepted the contribution agreement.

[sonarqubecloud]

Quality Gate passed

Issues
8 New issues
0 Accepted issues

Measures
0 Security Hotspots
88.1% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud