Review Java snippets for Pending Doc Ids

I added a snippet to show PendindDocIDs and IsDocumentPending in action. So, can you review the Java(Ish) code in commit … 3a57b76

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The Pending Doc Id feature must be documented under https://docs.couchbase.com/couchbase-lite/current/swift/learn/swift-replication.html#replication-status

Briefly describe its purpose and a code snippet for each platform