bug#37932: [PATCH] Support hidpi fringes and images with Cairo

[Carlos Pita]

I think I'm going to attempt scaling the fringe bitmaps in a generic
way as first suggested in #37689 [1], so as to get rid of the cairo
dependency. But, even if not a logical dependency, the organization of
that code would depend on the outcome of #37755 [2], which I had
closed in the tracker but now reopened in my mind, as shown by my last
post there :)

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[1] https://debbugs.gnu.org/cgi/bugreport.cgi?bug=37689
[2] https://debbugs.gnu.org/cgi/bugreport.cgi?bug=37755