Add rule no-case-declarations

[jusguy]

Adds the rule no-case-declarations.

Ecosystem impact:

1..186
# tests 186
# pass  185
# fail  1

Failing packages:

• bittorrent-tracker (Wrap lexical declarations inside switch cases webtorrent/bittorrent-tracker#305)

References:

• ESLint documentation for no-case-declarations
• Closes enable rule no-case-declarations to prevent usage of undeclared variables standard#1211

[jusguy]

Rule addition now has no impact.

1..186
# tests 186
# pass  186

# ok

[feross]

One repo started failing, but I PR'd it: zensh/resp.js#3

[feross]

Let's ship this in standard v14

[mightyiam]

Oh, wow. I didn't even realize that the code after case foo: is not a block. And that I could simply add a block there. Lovely. Excellent rule, it seems.

[feross]

@mightyiam Yeah, this blew my mind as well when I discovered it. Now I always use blocks in case statements.

[feross]

@justinkalland Btw, thanks for the pull request! You're awesome! 🤩

[ungoldman]

Just discovered this rule from upgrading to standard 14 and grumbled until I read https://eslint.org/docs/rules/no-case-declarations and learned something new. Thank you! I feel like each of these rules deserves its own class or blog or something, so much to learn about here. Okay good night 👋

[feross]

@ungoldman Indeed! Perhaps we can add such explanations to the RULES.md file!