Partially migrate completion to Rubydex #16916

Job	Run time
lint_node	33s
Verify Jekyll website builds	12s
lint_ruby	28s
build_node (macos-latest)	2m 39s
build_node (ubuntu-latest)	2m 26s
Ruby 3.3 on macos-latest	6m 36s
Ruby 3.3 on ubuntu-latest	8m 4s
Ruby 4.0 on macos-latest	4m 59s
Ruby 3.3 on windows-latest	20m 41s
Ruby 3.4 on ubuntu-latest	9m 42s
Ruby 3.4 on windows-latest	22m 28s
Ruby 4.0 on ubuntu-latest	7m 17s
Ruby 4.0 on windows-latest	21m 2s
Ruby 3.4 on macos-latest	4m 40s
build_node (windows-latest)	5m 13s
	1h 57m 0s

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