Instead of registering the font via CTFontManagerRegister we just create
a font descriptor for the data/URL and populate that like normal system
fonts. This makes the code more similar to how we deal with other fonts,
shaves off a ms during font registration due to not registering the font,
and fixes an issue on iOS where CTFontManagerRegister would invalidate
earlier populated system font descriptors.
Task-number: QTBUG-56765
Change-Id: I002a65075b15837c9a2d22573020d4c834111837
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>
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