Twenty Nineteen: Consider syncing up font smoothing between the front end and block-based editor

[laurelfulford]

This was originally reported by @kjellr in Twenty Nineteen's GitHub repo:

Currently, the front end of the site implements font smoothing via the following rules:

-webkit-font-smoothing: antialiased;
-moz-osx-font-smoothing: grayscale;

These rules do not exist in the Gutenberg editor. This leads to a much heavier display of text in the editor than in the front end.

This will need to be scoped in such a way that it doesn't bleed out of the actual content in the editor into block-level controls/placeholder labels/menu text/etc.

Original ticket: ​https://github.com/WordPress/twentynineteen/issues/281

[laurelfulford]

Twenty Nineteen - how the fonts appear on the front-end

[laurelfulford]

Twenty Nineteen - how the fonts now appear in the editor - noticeably heavier