Fix Layout/EmptyLineBetweenDefs error with endless methods

[dvandersluis]

Previously, Layout/EmptyLineBetweenDefs would error when encountering an endless method because node.loc.end is nil when endless. Now the end position for an endless method can be calculated. If AllowAdjacentOneLineDefs is true, endless methods are treated like single-line methods.

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[dvandersluis]

@bbatsov it’d be good to merge this before the “ruby 3” release cause this is an actual error raised by rubocop when endless methods are encountered.

[bbatsov]

Done!