Implements `if_none` and friends (#875) #3459

Job	Run time
Setup Build Matrix (true, ion-rust, windows, macos, ubuntu, al2-x86, al2-arm, windows, macos, ubu...	1s
Build and Test (windows, default)	5m 41s
Build and Test (windows, all)	5m 46s
Build and Test (windows, experimental-ion-hash)	6m 24s
Build and Test (windows, experimental)	7m 9s
Build and Test (macos, default)	1m 50s
Build and Test (macos, all)	2m 27s
Build and Test (macos, experimental-ion-hash)	2m 47s
Build and Test (macos, experimental)	2m 22s
Build and Test (ubuntu, default)	2m 10s
Build and Test (ubuntu, all)	4m 24s
Build and Test (ubuntu, experimental-ion-hash)	2m 32s
Build and Test (ubuntu, experimental)	3m 0s
Build and Test (al2-x86, default)	1m 38s
Build and Test (al2-x86, all)	2m 17s
Build and Test (al2-x86, experimental-ion-hash)	1m 55s
Build and Test (al2-x86, experimental)	2m 15s
Build and Test (al2-arm, default)	1m 38s
Build and Test (al2-arm, all)	2m 5s
Build and Test (al2-arm, experimental-ion-hash)	1m 42s
Build and Test (al2-arm, experimental)	2m 3s
Build and Test Confirmation	1s
	1h 2m 7s

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