Add EntryStream.collapseKeys(): collapse adjacent elements with the equal key

Question

Three signatures are proposed:

// collapse elements with the same key gathering corresponding values to list
EntryStream<k list>> collapseKeys();

// collapse elements with the same key reducing the values with given mergeFunction
EntryStream<k v> collapseKeys(BinaryOperator<v> mergeFunction);

// collapse elements with the same key reducing the values with given Collector
<a r> EntryStream<k r> collapseKeys(Collector<v a r> collector);
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• [x] Implementation
• [x] Tests
• [x] JavaDoc
• [x] Changes
• [x] Cheatsheet

该提问来源于开源项目：amaembo/streamex