Update Style/SingleLineMethods to correct to an endless method definition if they are allowed

[dvandersluis]

Follows #9281.

If Style/EndlessMethod is enabled and not using the disallow style, single line methods will be corrected to endless methods instead. My rationale here is that if the user is allowing endless methods, they are a "smaller" correction for single line methods than replacing with a normal method definition.

I went back and forth about if this should be configured independently from the Style/EndlessMethod configuration. I think it makes sense to keep all the configuration for endless methods in one place, but if we'd rather have it specifically configured for Style/SingleLineMethods, I'd be happy to make that change.

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[dvandersluis]

Once #9281 is merged I'll rebase its commit out of this PR, but it's needed to make the tests pass.

[bbatsov]

@dvandersluis Please, take a moment to rebase this PR when you can.

[dvandersluis]

@bbatsov definitely, done!

[bbatsov]

Thanks!