[Conformance test] Examples for linkMerge merge_flattened

[bogdang989]

Conformance tests covering linkMerge method merge_flattened (and maybe also merge_nested) on nested array input with more that one level of nesting are not available, might be worth adding.

[kinow]

Selected one issue from the Barn Raising wiki randomly, and got this one :-) Can I try to write these conformance tests? I'm not familiar with linkMerge and merge_flattened, so it looks like I'd learn about these while writing the test too. Thanks!