Improve MobileCore setApplication docs

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Which topic?

https://developer.adobe.com/client-sdks/home/base/mobile-core/lifecycle/#register-lifecycle-with-mobile-core-and-add-appropriate-startpause-calls

### What's wrong with the content?

Missing import, or unclear examples on how the application instance can be retrieved for the usages of the MobileCore.setApplication API.

### What changes do you propose?

Update all examples on setApplication(...) and indicate the application instance needs to be passed as a parameter. May include link to Android dev docs like Activity#getApplication or examples depending on the surrounding context such as
`MobileCore.setApplication(this)` or `MobileCore.setApplication(activity.getApplication())`

### Anything else that can help to cover this?

_No response_