Adding `checkAndUpdateUnsentReports` from iOS API to android crashlytics too

## What feature would you like to see?

The crashlytics iOS API provides a neat API to modify reports (like adding extra custom keys etc.), after the crash happened. (See the documentation [here](https://firebase.google.com/docs/reference/swift/firebasecrashlytics/api/reference/Classes/Crashlytics#checkandupdateunsentreports))
The android API seems to be missing this function for some reason. It would be helpful, if the android API would provide such functionality too.

## How would you use it?
I want this feature to be able, to match a user report to a crashlytics crash report. If the user encounters a crash, they are left with the choice to report that error. If they report that error, the user gets a generated report id, which they can give to us. The generated report id will be attached to the crashlytics crash report through the custom keys. This allows us to better investigate errors through communication with the user. This process works well on iOS, android is sadly missing the API.

The only workaround that I can think of is, always setting a report id as custom key at the start of the app. Then writing this report id to disk so it persists through a crash. And then read it back from disk, if the user wants to report the crash.
However, this is rather inconvenient.