Auto-Instrument onResume in Activity transactions

[romtsn]

Description

We could create spans for each of the callbacks to better surface the performance of each method if they involve some heavy computations (similar to how sentry-cocoa does it for viewDidLoad, viewDidAppear and so on).

Android API 29 and above have new callbacks in the AcitivtyLifecycleCallbacks class (onActivityPreCreated/onActivityPostCreated and friends), so we could utilize them when implementing it.

[markushi]

Let's start small and use the existing API 29+ callbacks in the first iteration. And it could be a good chance to refactor our ActivityLifecycleIntegration.

[stefanosiano]

Let's schedule it for the next quarter @kahest

[stefanosiano]

let's discuss if we want to do it, as it could be "spammy", and if we want to do it for app start transactions or for all activities.
Based on the changes of warm start PR, all the logic would be inside our ActivityLifecycleIntegration, and it would be fairly easy to do (currently we have onCreate and onStart spans only for app start transactions)