Swift

Add comparison operators for `CodingKey` #89

Job	Run time
macOS (release)	15m 54s
macOS (debug, SWIFT_BUILD_DYNAMIC_LIBRARY=1)	1m 21s
Android (6.1, x86_64)	4m 32s
macOS (debug)	1m 49s
Linux (swift:6.0.3, debug)	1m 56s
Linux (swift:6.0.3, release)	13m 54s
macOS (release, SWIFT_BUILD_DYNAMIC_LIBRARY=1)	12m 54s
Android (nightly-6.2, x86_64)	2m 51s
Linux (swift:6.1.2, release)	12m 27s
Android (6.1, aarch64)	3m 6s
Linux (swift:6.0.3, release, SWIFT_BUILD_DYNAMIC_LIBRARY=1)	13m 6s
Android (nightly-6.2, aarch64)	3m 42s
Linux (swift:6.1.2, debug)	1m 54s
Linux (swift:6.0.3, debug, SWIFT_BUILD_DYNAMIC_LIBRARY=1)	2m 5s
Linux (swift:6.1.2, release, SWIFT_BUILD_DYNAMIC_LIBRARY=1)	12m 32s
Linux (swift:6.1.2, debug, SWIFT_BUILD_DYNAMIC_LIBRARY=1)	1m 56s
	1h 45m 59s

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