File I/O APM GA

[philipphofmann]

Ship the feature turned off by default and mark is at experimental with a code comment:

• [x] https://github.com/getsentry/sentry-cocoa/issues/1609
• [x] https://github.com/getsentry/sentry-cocoa/issues/1610
• [x] Where to put the file size https://github.com/getsentry/develop/issues/463#issuecomment-972722409
• [x] #1607
• [x] #1646
• [ ] Instrument overhead of APM of file IO
• [x] https://github.com/getsentry/sentry-docs/pull/4937
• [ ] In a major or minor bump enable the feature flag.

[philipphofmann]

Testing Strategy

Risks

1. Introduce a bug to NSData without crashing
2. Crashing apps
3. False added spans or not added spans
4. All of the above only could occur on specific OS versions

Mitigation for Alpha

• [x] Mitigates 3. Unit tests for the SpanTracker classes. Done in https://github.com/getsentry/sentry-cocoa/pull/1557
• [x] Mitigates 4 and 2. https://github.com/getsentry/sentry-cocoa/issues/1611

Mitigation for Beta

• [x] Mitigates 1, 2, 4. https://github.com/getsentry/sentry-cocoa/issues/1612
• [x] Mitigates 1, 2, 4. https://github.com/getsentry/sentry-cocoa/issues/1613
• [x] Mitigates 1, 2, 3. Integration tests for all swizzled methods of NSData to make sure the correct spans are created, we don't cause a crash and NSData is working properly after swizzling. Done in https://github.com/getsentry/sentry-cocoa/pull/1557

Mitigation for GA

• [ ] Instrument overhead of APM of file IO

[philipphofmann]

Is already GA with #2212.

Enable by default see https://github.com/getsentry/sentry-cocoa/issues/2264