[Fix #7739] Allow methods raising NotImplementedError in Lint/UnusedMethodArgument

[tejasbubane]

Closes #7739

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[bbatsov]

Apart from my small remarks I'm fine with the proposed changes.

[bbatsov]

Thanks!

[sandstrom]

@tejasbubane Awesome addition!

What do you think about Lint/UnreachableCode having this check too?

Basically such that it would allow:

def my_method
  raise NotImplementedError
  
  1 + 1
end