Autosuggest font names in customizer and editor

[seasick]

Is your feature request related to a problem? Please describe.

Selecting the font is a gamble. When I select the fonts section in the left bar, it would be nice to see the names that can be used in the script.

Describe the solution you'd like

• Use a full fledged editor instead of a textarea (e.g. CodeMirror, Monaco)
• Editor suggests usable fonts when I type them in
• Customizer shows input suggestions for font names