Build/Test Tools: Enable JSDocs to be linted with ESLint.

As part of the [Javascript Inline Docs Initiative](https://make.wordpress.org/core/handbook/docs/inline/js/) this add some tooling to lint Javascript docblocks. Two new commands:

* `npm run lint:jsdoc`
* `npm run lint:jsdoc:fix`

The latter will run the linter and try to fix an possible issues automatically.

Fixes #43828.
Props netweb, atimmer, kamataryo, whyisjake.


Built from https://develop.svn.wordpress.org/trunk@48650


git-svn-id: https://core.svn.wordpress.org/trunk@48412 1a063a9b-81f0-0310-95a4-ce76da25c4cd