Emit `transaction.data` inside `contexts.trace.data`

[cleptric]

We need to ensure that transaction.data is sent as contexts.trace.data so we can also attach/extract metrics from transaction data.

## SDKs
- [x] JavaScript SDK
- [x] Electron SDK
- [x] Python SDK https://github.com/getsentry/sentry-python/issues/3372
- [x] PHP SDK
- [x] Laravel SDK
- [x] Symfony SDK
- [x] Ruby SDK https://github.com/getsentry/sentry-ruby/issues/2363
- [x] Capacitor SDK
- [x] Cordova SDK
- [ ] Go SDK https://github.com/getsentry/sentry-go/issues/863
- [ ] https://github.com/getsentry/sentry-cocoa/issues/4248
- [ ] https://github.com/getsentry/sentry-java/issues/3626
- [ ] https://github.com/getsentry/sentry-react-native/issues/4011
- [ ] Elixir SDK
- [ ] Rust SDK
- [ ] Java SDK
- [ ] .NET SDK
- [ ] Unity SDK
- [ ] Unreal SDK
- [ ] PowerShell SDK
- [ ] https://github.com/getsentry/sentry-dart/issues/2257
- [ ] Flutter SDK
- [x] ~Kotlin Multiplatform SDK~
- [ ] Native SDK
- [ ] Sentry CLI

[jan-auer]

Example usage for this in Python is:

with scope.start_transaction(name="hello"):
    span_or_tx = sentry_sdk.get_current_span()
    span_or_tx.set_data("foo", "bar")

[Lms24]

I checked for JS and we don't set transactionEvent.data at all, but only transactionEvent.contexts.trace.data. Is this alright?

(Fwiw, in JS we no longer have setData or setTag APIs but only setAttribute which always populates span.data for child spans or event.contexts.trace.data for the root span (i.e. transaction event))

[jan-auer]

@Lms24 yes, that's the right way. We expect root span data (i.e. span data of the transaction) to be placed into contexts.trace.data.

There is no data field on transactions. I believe @cleptric is referring to transaction._data in the case of the Python SDK, which is the transaction's own span's data.

[cleptric]

In some SDKs, transactions are inherited from span and, therefore, have a data property. The change we need to make is to attach this data to the transaction envelope item payload under contexts.trace.data.

[krystofwoldrich]

@Lms24 From which JS SDK version is event.contexts.trace.data populated? Is this part of v7 or only v8?

[Lms24]

As far as I know from both versions. I don't recall making any changes there for v8

[lucas-zimerman]

Capacitor should be marked as ok since it relies on the JavaScript SDK for that. I will double-check the Cordova one

[markushi]

@cleptric sentry-java currently sets transactionEvent.data as transactionEvent.extra (see comment here) - should we still do that or simply move it all to contexts.trace.data?

[cleptric]

Please move it, extra should not be used by SDKs anymore.

[lbloder]

Please move it, extra should not be used by SDKs anymore.

@cleptric Could you clarify what is meant by this? Does this mean we should remove extra completely (i.e. remove it from the SentryEvent class) or just not set any data to extras but keep it so that users can write to it?

[cleptric]

We can keep any setExtra() etc. APIs but the SDK should not add any data automatically onto extra.

[lucas-zimerman]

Finished checking Cordova and the data is correctly set.