CDRIVER-2206 Expose is_default() in public API for read and write concerns

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• Closed

PHPC-977 Upgrade libbson and libmongoc to 1.7.0

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• Closed

PHPLIB-261 Omit default read and write concern from commands

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• Closed

CDRIVER-2273 Do not include default write concern in insert, update, and delete commands

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• Closed