Allow capital L as variable name

[tbu-]

Allow capital L as variable name

When the lint uppercase_variables is disallowed/warned about/denied, an
uppercase L (ell) should be still allowed as its lowercase variant is too
similar to an uppercase i or an 1 (one).

[emberian]

This doesn't make sense to me. "Disallow uppercase variables, except this random one-character one"

[tbu-]

Well, the point is that you can have all the small latin letters from a-z as single-character variable names, except for the small L, which is why it is used in its capital form in some codebases.

letI = 0;let l = 0;let k = I + l + 1;

See for example the above negative-example.

[tbu-]

If this still does not make sense to you, feel free to close this pull request. :)

[emberian]

I'm more inclined to say "use different variable names" than "add corner case to lint", but I'll leave it to someone else to decide about this PR.

[alexcrichton]

I think that this is a niche enough use case that already has enough controls over it that it's not that necessary.

Thanks for the PR, though!

[huonw]

(The work-around of just allowing it would be helped by #12963 which I just opened.)