chore(firestore): add support for onSnapshotsInSync

[SelaseKay]

Description

Currently the firebase-js-sdk has an onSnapshotsInSync API and react-native-firebase does not

This PR (when complete) will close that feature gap)

Related issues

Release Summary

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
  • Yes
• My change supports the following platforms;
  • Android
  • iOS
  • Other (macOS, web)
• My change includes tests;
  • e2e tests added or updated in packages/\*\*/e2e
  • jest tests added or updated in packages/\*\*/__tests__
• I have updated TypeScript types that are affected by my change.
• This is a breaking change;
  • Yes
  • No

Test Plan

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[mikehardy]

Just curious - is this a namespace -> modular gap, or a feature gap between RNFB and firebase-js-sdk?

There's no info in the PR beyond the boilerplate template contents

[SelaseKay]

@mikehardy, it's a feature. onSnapshotsInSync is not supported in RNFB, both in the JS and natively. This PR is not complete.

[mikehardy]

Ah, thanks. I updated the description to match in case I take a peek again