feat(useMergeRefs): add option to merge two or more refs #55

Job	Run time
Unit, component and e2e tests (18.x, ubuntu-latest)	3m 15s
Unit, component and e2e tests (20.x, ubuntu-latest)	3m 23s
Deploy documentation	1m 16s
Publish to npm (20.x)	42s
	8m 36s

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