Add order-in-computed rule

[csordasmarton]

No description provided.

[ota-meshi]

Thank you for working on implementing this rule.
However, this rule conflicts with the vue/sort-keys rule, so I can't merge it as it is.
https://eslint.vuejs.org/rules/sort-keys.html

We need to think carefully about what we can do to avoid conflicts between sort-keys rule and the new rule.

[csordasmarton]

@ota-meshi Yes, you are absolutely right. So in this case I will close this PR.