[No Jira][v3] Adapt internal-testing-tools-package to v3

[sbarrio]

What does this PR do?

The DatadogSDKWrapper has changed a bit on v3, mainly removing it's core SDK instance reference. On the other hand, the Write protocol was modified slightly for v3 of iOS, so the FEatureScopeInterceptor used to track events on internal tests needed to be adapted.

Motivation

We need the internal testing module working to be able to test v3 with out e2e test suite.

Additional data

I tested the fix locally with the nightly tests project and the test app builds and runs properly after this change.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests
• Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)
• If this PR is auto-generated, please make sure also to manually update the code related to the change

[sbarrio]

Calling register directly with the same name does not overwrite its value, so we need to call unregsiterDefault first to be able to set the proxied core as the default core.

[sbarrio]

I removed these for two reasons:

• It's a bit weird that the logs module is checking for this when the native SDK does it too.
• When running the app with the internal testing tools module, this check will always be false, since the way in which the core SDK checks if the core is initialized is by checking the core type and comparing it with DatadogCore. Since the internal testing tools wrap it into a DatadogCoreProxy to allow for intercepting events this check always fails, even if the SDK is running fine.

And for those curious, this worked fine on v2 because the DatadogSdkWrapper kept a local reference to the core sdk instance, and the internal testing tools were wrapping that one instead, so calls to Datadog.isInitialized would still work fine as they would not deal with the wrapped core but with the internal SDK one.