Split and update caret.js for Chromium changes

[The-Compiler]

Chromium has had some changes in recent years for its caret browsing code:

https://chromium.googlesource.com/chromium/src/+log/main/ui/accessibility/extensions/caretbrowsing (note, page takes an eternity to load)

Since the initial implementation in b184d2f:

3e1a26c Update copyright headers in ui/, url/ by Avi Drissman · 1 year, 6 months ago
34bb210 Refactor caretbrowsing/storage.js and add tests by Anastasia Helfinstein · 2 years, 1 month ago
28fa2dd Add accessibility extension test base by Anastasia Helfinstein · 2 years, 1 month ago
17e1505 Extract independent node/selection functions in caret browsing extension by Anastasia Helfinstein · 2 years, 2 months ago
abd3b15 Update comments in the caretenhancer extension by Anastasia Helfinstein · 2 years, 2 months ago
399e5ce Consolidate storage logic in caret browsing extension into a class by Anastasia Helfinstein · 2 years, 2 months ago
82b0912 Clean up caret browser extension for loops by Anastasia Helfinstein · 2 years, 2 months ago
a9952eef Migrate caret browser extension to manifest v3 by Anastasia Helfinstein · 2 years, 2 months ago
59c2a4a Convert caret browsing extension to an ES6 style class by Anastasia Helfinstein · 2 years, 2 months ago
05cb1be Update caret browsing extension to replace var with const/let by Anastasia Helfinstein · 2 years, 2 months ago
9857a74 Migrate Caret Browsing extension to use service workers by Anastasia Helfinstein · 2 years, 2 months ago
62b139f Add BUILD file for Caret Browsing extension, update one string. by Dominic Mazzoni · 4 years, 5 months ago

I also think we should aim to split the file into multiple JS files, to mirror the Chromium structure. Finally, we should probably avoid/revert style-only changes we did in comparison to upstream, to allow for easier diffing...

Since we diverge a lot, not sure yet what the best strategy for this would be. Try to reimplement Chromium's changes manually on top of ours? Start with the current Chromium codebase and try to get our changes in again?