Highlight GUI: List only monospaced fonts

In the GUI dropdown menu for choosing the font, all system-installed fonts are currently listed, which results in a very long list that includes mostly fonts which are useless for visualizing code (including dingbats, icon fonts, Hebrew, Arabic and Chinese fonts).

It would be useful to limit the listed fonts only to monospaced fonts, which would reduce drastically the number of entries (from hundreds, down to a few dozens).