feat: Add no-exclusive-tests rule

[RoryH]

Adds rule similar to other test frameworks to identify exclusive tests.

https://mochajs.org/#exclusive-tests

[jennifer-shehane]

I like it.

[kuceb]

@RoryH Thanks this is great. I agree its definitely needed, but we should probably just use https://github.com/lo1tuma/eslint-plugin-mocha. There are other useful rules in there too like no-indentical-title and no-nested-tests (and we could mutate the error messages to say Cypress instead of mocha if we wanted).

We obviously wouldn't want to use it as a plugin however since users would have to install both plugins, which would be awful.

What do you think, would you find any of those other rules useful @RoryH?

[RoryH]

@bkucera I had considered possibly re-using eslint-plugin-mocha somehow but this is my first time diving into eslint plugins 🤓 . How do you see it working without adding it as an extra dependency, would it be transitive dependency of eslint-plugin-cypress?

[kuceb]

@RoryH we add it as a dependency, but we require the rules directly, like they do in this file https://github.com/lo1tuma/eslint-plugin-mocha/blob/master/index.js

[RoryH]

I like it... If you guys are happy I'll close this PR and open a new one pulling in the rules from eslint-plugin-mocha module 👍

[kuceb]

@RoryH sounds great