[MacPorts] #60511: gtk3, pango and cairo: move to quartz as default backend

[MacPorts]

#60511: gtk3, pango and cairo: move to quartz as default backend
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 Reporter:  ra1nb0w      |      Owner:  dbevans
     Type:  enhancement  |     Status:  assigned
 Priority:  Normal       |  Milestone:
Component:  ports        |    Version:
 Keywords:               |       Port:  gtk3, pango, cairo
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 What do you think to make {{{quartz}}} the default backend for gtk3, pango
 and cairo? At least for the 3-4 latest versions of macOS.
 I am using it from many years and it seems to work quite well with many
 applications (inkscape and gimp official distribution are using that).
 Note {{{gtk2}}} requires {{{pango}}} and it should remain to x11 (at least
 to me, it works fine with quartz except for gEDA) therefore we should
 manage the different bakend.

 ps. this idea born during the process of updating GNURadio to the 3.8
 version.

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Ticket URL: <https://trac.macports.org/ticket/60511>
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