refactor(types/operator): rename is_exist to exists #1858

Job	Run time
build_all_features	4m 35s
build_all_platforms (ubuntu-latest)	2m 28s
build_default_features (ubuntu-latest)	42s
build_all_platforms (macos-latest)	2m 12s
build_under_wasm	59s
build_default_features (macos-latest)	35s
build_all_platforms (windows-latest)	4m 48s
build_default_features (windows-latest)	2m 11s
check_clippy	3m 29s
check_docs	3m 12s
check_msrv	32s
unit	6m 32s
	32m 15s

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