Bug 1993974 - [devtools] Add proper JsDoc in devtools/shared/css/parsing-utils.js. r=devtools-reviewers,frontend-codestyle-reviewers,jdescottes.

We add a ParsedDeclaration JSDoc typedef for all the `parse*Declarations` function.
And while we're at it, we enable the jsdoc eslint rules for parsing-utils.js, and
fix the issues that were raised by eslint.

Differential Revision: https://phabricator.services.mozilla.com/D268390

UltraBlame original commit: 7b26d0479ace34748427c234f5ac8791117a802e

Author: marco-c