Add deduplicate_entry_values mode to TableFlattener.

This CL introduces DeduplicateItemsResEntryWriter which stores unique
pairs of entry and value and deduplicates a new pair based of this data
before writing it into the buffer.

Bug: b/249793372
Test: ResEntriesWriter_test, TableFlattener_test
Change-Id: I938a3425a87bfad9853e59193680de2050a95bd2