Add parity methods to Protobuf Repeated and Map

Added fns like first(), last(), contains_key() and implement
standard traits that are supported by Vec (DoubleEndedIterator, FromIterator).

PiperOrigin-RevId: 910689041

Protobuf Team Bot committed 1mo ago

f472fe1724ccaf4055f773439f3145f90e419740

Parent: 2b15f7c

Committed by Copybara-Service <copybara-worker@google.com> on 5/5/2026, 3:00:20 PM