Add RBS files and tests #35

Job	Run time
ruby-versions / Generate Ruby versions	2s
build (2.5 / ubuntu-latest)	17s
build (2.5 / macos-latest)	19s
build (2.5 / windows-latest)	18s
build (2.6 / ubuntu-latest)	19s
build (2.6 / macos-latest)	20s
build (2.6 / windows-latest)	19s
build (2.7 / ubuntu-latest)	18s
build (2.7 / macos-latest)	15s
build (2.7 / windows-latest)	15s
build (3.0 / ubuntu-latest)	16s
build (3.0 / macos-latest)	15s
build (3.0 / windows-latest)	19s
build (3.1 / ubuntu-latest)	20s
build (3.1 / macos-latest)	22s
build (3.1 / windows-latest)	14s
build (3.2 / ubuntu-latest)	10s
build (3.2 / macos-latest)	15s
build (3.2 / windows-latest)	17s
build (head / ubuntu-latest)	16s
build (head / macos-latest)	18s
build (head / windows-latest)	17s
	6m 1s

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