RUMM-731 Refactor URLSession instrumentation to support RUM and Tracing

[ncreated]

What and why?

⚙️ This PR applies refactoring to the URLSession instrumentation code. Given the requirements of the RUM product, previous implementation didn't scale well to support the URLSessionDelegate, which is necessary to retrieve network task metrics.

With this refactoring:

• we instrument all 4 URLSession.dataTask(with:) creation methods (vs only 2 before);
• request timing information is read directly from URLSessionTaskMetrics object (vs measured in swizzled code);
• the integration with Alamofire will now be possible (our delegate can be used in Alamofire.EventMonitor).

The impact of this refactoring was mitigated by adding integration tests last sprint, in #253.

How?

The URLSessionTask task is now observed by two objects:

• URLSessionSwizzler - to notify task creation and (in some cases) completion,
• DDURLSessionDelegate - to retrieve task metrics and (in other cases) notify the completion.

Both talk to the URLSessionInterceptor, where interception happens and tracing Span is created (through URLSessionTracingHandler).

Testing strategy is simple and it follows component relationships:

• URLSessionSwizzlerTests ensure that methods on URLSessionInterceptor are called properly,
• DDURLSessionDelegateTests ensure that methods on URLSessionInterceptor are called properly,
• URLSessionInterceptorTests ensure that the Span is send to the backend on given circumstances,
• URLSessionTracingHandlerTests assert the values of produced Span.

Although this PR seems big, only its first commit relates to the actual implementation. The rest is duplication of test cases in different scenarios (with 2 new instrumented URLSession methods, we have way more cases than before).

Review checklist

• Feature or bugfix MUST have appropriate tests (unit, integration)
• Make sure each commit and the PR mention the Issue number or JIRA reference

[buranmert]

i haven't looked at tests yet but i guess we can discuss those non-major issues first