Allow to include all threads for non-fatal exceptions

## What feature would you like to see?

I suggest to add an extra argument `includeAllThreads` to `recordException`:
```
public class FirebaseCrashlytics
{
...
public void recordException(Throwable throwable, boolean includeAllThreads)
...
}
```

## How would you use it?

We are investigating ANRs using ANR-WatchDog library.
The default behaviour of the `ANRWatchDog` class is to throw unhandled exception which crashes the app after `main` thread is blocked for the specified amount of time. When it happens Crashlytics collects all threads stack-traces and produces a Fatal crash report.

This behaviour naturally boosts crash-rate of the app what is not good. But when I handle `ANRWatchDog`'s exception to record it using `FirebaseCrashlytics.recordException` it does not include other threads stack-traces by design. So basically such non-fatal crash report is useless in ANR investigations.

I would like to force Crashlytics to collect all threads stack-traces and produce full crash report for a non-fatal exception.