Fix CJK fonts again and misc. font issues (#14575)

Fix CJK fonts again and misc. font issues (#14575)

* Push system-ui further down the stack, fix #12966

* Fix Firefox showing U+300x in emoji font and more

* Revert emoji font and fix long-standing Safari bug

* Exclude Safari emoji fix above 1.25x zoom

* Minor correctness/typo fix, affects only legacy platforms

* Emoji consistency for monospace (e.g. EasyMDE)

* Override paradigm; macOS/iOS-specific metric fix

* Move whitespace fix to font-face

* Handle metric calculation errors with Firefox

* One last workaround for aliased fonts in Linux