[autocomplete-css] Update Completions, deps, improve completions data sources

[confused-Techie]

In this PR:

• Updated dependencies
• Removed mdn/content as a dependency due to incompatibility on older NodeJS versions and instead we download the repo's data manually.
• Improved data source for HTML nodes that can be targeted
• Found a methodology for updating pseudo-selectors, which we didn't have previously. (We just kept reusing the existing pseudo-selector completions rather than update them)
• Added a few missing items to our manual property description file. (Not all of them though, there's still 46 missing descriptions)
• Updated our COMPLETIONS.json file with all these new improvements.

It seemed it was about time to run an update of our completions, and I though I'd update our deps at the same time since they have become a bit out of date. Then while doing so found a few areas of improvements.

I wouldn't recommend manually reviewing the COMPLETIONS.json file too closely, as it's huge, and instead focusing on it's format for validity, and focusing more on the behavior of code.