Qt uses a default font size of 13pt for QWidgets on macOS. By setting
the default font size to 10pt, text becomes too small for comfortable
use on macOS.
This PR patches the font files copied into the macOS bundle to use a
larger font-size of 12pt. It also sets the fallback font to the more
modern SF Display-based `.AppleSystemUIFont` used by default in macOS
if Open Sans is not found.
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