Only update session tracking after Activities have changed state

[lemnik]

Goal

On SDK 29 and higher use the onActivityPostStarted and onActivityPostStopped to update the session tracking, ensuring the Activity has finished changing state before we fetch new session state attributes.

Design

When the foreground activities are started and stopped we capture flags such as context and inForeground and send them to observing layers (such as ReactNative and NDK). By capturing them after the onStart/onStop methods have returned we ensure that these attributes are properly up-to-date.

Testing

TBD

[bugsnagbot]

Android notifier sizes

Format	Size impact of Bugsnag (kB)	Size impact of Bugsnag when Minified (kB)
APK	1855.69	1606.18
arm64_v8a	651.66	401.8
armeabi_v7a	586.13	340.37
x86	725.37	475.51
x86_64	692.61	446.85

Generated by 🚫 Danger

[Cawllec]

LGTM! I'm quickly testing another test change for a very similar test-flake, so I'd hold off from merging just yet.