Add specs for IO::Buffer's bitwise operations #2322

Job	Run time
RuboCop	49s
specs (macos, 3.4.8)	1m 36s
specs (windows, 3.3.10)	3m 15s
specs (ubuntu, 3.3.10)	1m 29s
specs (ubuntu, 4.0.1, --parser=parse.y)	1m 39s
specs (ubuntu, 4.0.1, --enable-frozen-string-literal)	1m 32s
specs (ubuntu, 4.0.1)	1m 30s
specs (macos, 4.0.1)	1m 47s
specs (windows, 4.0.1)	3m 26s
specs (ubuntu, 3.4.8)	1m 48s
specs (macos, 3.3.10)	1m 33s
specs (ubuntu, 4.0.1, LC_ALL=C)	1m 35s
specs (ubuntu, 4.0.1, --repeat 2)	2m 21s
specs (windows, 3.4.8)	3m 30s
	27m 50s

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