Bump `bitflags` to v2 (#400) (#553) #655

Job	Run time
build (1.57.0, ubuntu-latest)	1m 19s
rustfmt	7s
powerpc_cross	10s
build (1.57.0, windows-latest)	1m 50s
feature_check (ubuntu-latest)	59s
build (1.57.0, macos-latest)	1m 29s
feature_check (macos-latest)	29s
test_all (ubuntu-latest)	3m 2s
build (stable, ubuntu-latest)	6s
feature_check (unstable, ubuntu-latest)	1m 1s
test_all (macos-latest)	2m 8s
build (stable, windows-latest)	1m 6s
feature_check (unstable, macos-latest)	30s
build (stable, macos-latest)	11s
feature_check (benchmarks, ubuntu-latest)	1m 1s
build (beta, ubuntu-latest)	15s
feature_check (benchmarks, macos-latest)	40s
build (beta, windows-latest)	26s
build (beta, macos-latest)	17s
build (nightly, ubuntu-latest)	13s
build (nightly, windows-latest)	41s
build (nightly, macos-latest)	18s
	18m 18s

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