Update: add fixer for no-undef-init

[not-an-aardvark]

What is the purpose of this pull request? (put an "X" next to item)

[ ] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[x] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

Please check each item to ensure your pull request is ready:

• I've read the pull request guide
• I've included tests for my change
• I've updated documentation for my change (if appropriate)

What changes did you make? (Give an overview)

This adds a fixer for no-undef-init.

The fixer replaces var x = undefined; with var x;. It does not apply a fix if destructuring is used, e.g. var [x] = undefined;

This PR also prevents no-undef-init from reporting errors if an undefined variable is declared in local scope, similar to no-console, no-alert, and no-regex-spaces.

Is there anything you'd like reviewers to focus on?

Nothing in particular.

[mention-bot]

@not-an-aardvark, thanks for your PR! By analyzing the annotation information on this pull request, we identified @vitorbal, @mysticatea and @kaicataldo to be potential reviewers

[eslintbot]

LGTM

[mysticatea]

LGTM, thank you!

[not-an-aardvark]

I'll champion this.