New port: x11-fonts/iosevka: Slender monospace sans-serif and slab-serif typeface for programming

Iosevka is a slender monospace sans-serif and slab-serif typeface inspired
by Pragmata Pro, M+ and PF DIN Mono, designed to be the ideal font for
programming.

It comes in regular, bold, italic and bold-italic with over 2000 Latin,
Greek, Cyrillic, phonetic and PowerLine glyphs. A IosevkaCC variant is also
provided, with several symbols enwiden, to be compatible with most CJK
typefaces.

WWW: https://typeof.net/Iosevka/

Reviewed by: mat
Approved by: mat (mentor)
Differential Revision: https://reviews.freebsd.org/D18873