Respond to code review
Respond to code review

- failedSyncCount -> this._failedSyncCount
- Reset at a point which is more obviously after a successful sync, and add comments to clarify the recursive syncage.
- Sync state will now flip from RECONNECTING to ERROR after FAILED_SYNC_ERROR_THRESHOLD syncs

matrix-org/matrix-js-sdk,matrix-org/matrix-js-sdk,krombel/matrix-js-sdk,krombel/matrix-js-sdk,matrix-org/matrix-js-sdk,matrix-org/matrix-js-sdk,krombel/matrix-js-sdk