New: sort-keys rule (fixes #6076)

[mysticatea]

Fixes #6076.

This PR adds sort-keys rule.

• This PR is sharing 1st commit d02e595 with Update: add props option to no-self-assign rule (fixes #6718) #6721. This commit adds astUtils.getStaticPropertyName function.
• This sort-keys implement sorts simple computed properties (e.g., let obj = {a: 1, [b]: 2}) similar to JSCS. This would help a use of symbols.
• This sort-keys implement ignores non-simple computed properties (e.g., let obj = {a: 1, [b + c]: 2}).
• I ported most tests from JSCS.
• I added a dependency, natural-compare, JSCS are using.

[mention-bot]

@mysticatea, thanks for your PR! By analyzing the annotation information on this pull request, we identified @nzakas, @cschuller and @aubergine10 to be potential reviewers

[eslintbot]

Thanks for the pull request, @mysticatea! I took a look to make sure it's ready for merging and found some changes are needed:

• Pull requests with code require an issue to be mentioned at the end of the commit summary, such as (fixes #1234). Please update the commit summary with an issue (file a new issue if one doesn't already exist).

Can you please update the pull request to address these?

(More information can be found in our pull request guide.)

[eslintbot]

Thanks for the pull request, @mysticatea! I took a look to make sure it's ready for merging and found some changes are needed:

• Pull requests with code require an issue to be mentioned at the end of the commit summary, such as (fixes #1234). Please update the commit summary with an issue (file a new issue if one doesn't already exist).

Can you please update the pull request to address these?

(More information can be found in our pull request guide.)

[eslintbot]

Thanks for the pull request, @mysticatea! I took a look to make sure it's ready for merging and found some changes are needed:

• Pull requests with code require an issue to be mentioned at the end of the commit summary, such as (fixes #1234). Please update the commit summary with an issue (file a new issue if one doesn't already exist).

Can you please update the pull request to address these?

(More information can be found in our pull request guide.)

[mysticatea]

The last commit has (fixes #6076).

[nzakas]

Can this be sensitive so it's not a negated term?

[platinumazure]

Or maybe caseSensitive for clarity?

[mysticatea]

Hmm, in that case, is the default behavior below or both false?

{
    "sort-keys": ["error", "asc", {"caseSensitive": true, "natural": false}]
}

[nzakas]

@markelog @mdevils @mikesherov can you guys look this over to compare with JSCS rule?

[eslintbot]

LGTM

[mysticatea]

I just updated an option: insensitive → caseSensitive

[eslintbot]

LGTM

[mysticatea]

Rebased for #6870.

[nzakas]

LGTM