Bug 1881821 - Clean up tokens files ahead of JSON source of truth setup r=desktop...

Bug 1881821 - Clean up tokens files ahead of JSON source of truth setup r=desktop-theme-reviewers,reusable-components-reviewers,hjones,dao,mstriemer

Changed
* `--color-background-*` are now part of the group of `--background-color` tokens
* `--box-background-color` is now part of the group of `--background-color` tokens as `--background-color-box`
* `--color-canvas` is now part of the group of `--background-color` tokens as `--background-color-canvas`
* `--border-interactive-*` are now part of the group of `--border-color` tokens and consequently now start with `--border-color`
* `--color-error-outline` is now an outline-specific token as `--outline-color-error`
* Comment headings were cleaned up as to follow the existing standard
* Better documentation behind the difference of "Base", "Application", and "Component" tiers in the design tokens documentation
* Tokens files are alphabetized

Removed
* `--outline-color-error` had duplicates in both high contrast mode media queries, so its value under `forced-colors` was removed
* "Base" and "Application" headings in tokens files were removed in order to lean in on the alphabetical order organization of token groups and promote a cleaner file and less confusion
* Documentation was edited down to not incude any guidance that we don't adhere to
* Remove duplicate interactive border color high contrast mode tokens in `tokens-brand.css` in favor of `tokens-shared.css`
* Remove `--button-border-color-primary` duplicate in `tokens-brand.css`
* Remove duplicate `--button-text-color` in `tokens-shared.css`

Differential Revision: https://phabricator.services.mozilla.com/D202767