Add regexp/no-extra-lookaround-assertions rule

[ota-meshi]

close #481

[fisker]

How about regexp/no-useless-assertions?

[ota-meshi]

The description of no-useless-assertions says:

Some assertion are unnecessary because the rest of the pattern forces them to always be accept (or reject).

The new rule don't report always accept/reject patterns, so I think the rules have different goals.

[ota-meshi]

@RunDevelopment Thank you for the your review!
I made changes to this PR. Could you please check again?

[RunDevelopment]

Thank you @ota-meshi.

I think the rule is implemented correctly, but I think the name/message might be a little confusing. The name "no useless lookaround assertions" and the message "This assertion is useless." might make it seem like reported assertions can be removed. E.g. (?=foo(?=bar)) -> (?=foo). Obviously, this is not what we mean, but I worry that some users might understand that way.

Maybe we could change the message to something like "This assertion is useless and can be inlined" or "This assertion is useless and can be converted into a group"? If we go with those messages, then we should probably also update the docs to use this language too. What do you think?

[ota-meshi]

I think the message you suggested is good! I will change it to use that message.

Do you have other good ideas for rule name?
What do you think about naming it no-extra-lookaround-assertions, in reference to no-extra-parens?
https://eslint.org/docs/latest/rules/no-extra-parens

[RunDevelopment]

What do you think about naming it no-extra-lookaround-assertions, in reference to no-extra-parens?

That is a really good idea! Let's go with that.

[ota-meshi]

I have changed this PR. Could you please check again?

[RunDevelopment]

Thank you @ota-meshi!