Documenting the titlebar-area-* env variables (#14035)

* Added compat data for individual env variables

The CSS env() function was introduce for the safe-area-inset-* variables only.
But these are no longer the only ones to exist.
Since I'm adding some MDN docs about the titlebar-area-* vars, I'd like the BCD data to give more specific compat data about those.

I introduced a section for the safe-inset-area-* vars and copied the same compat data from the env() section, since I think both were introduced at the same time.

And I added a section for the titlebar-area-* vars.

* Corrected versions

After checking the chromium CLs where this landed, I corrected the version numbers for chrome and edge, and added a note about linux (which came 1 release later).

I also used https://github.com/mdn/browser-compat-data/blob/main/browsers/opera.json and https://github.com/mdn/browser-compat-data/blob/main/browsers/opera_android.json to derive the Opera versions.

* Removed the alternate name for safe-area-inset

* Fixed syntax issue

* Addressed code review comments