Use cairo_surface_t rather than the deprecated GdkPixbuf for exported API

Note: we're still using GdkPixbuf as a file loader as cairo can only really
import PNGs rather than all the types supported in AppStream.
1 job for wip/hughsie/cairo_surface_t in 9 minutes and 54 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build
failed #155255
build-gnome-software

00:09:54

 
Name Stage Failure
failed
build-gnome-software Build
(gs-self-test-core:1923): Gtk-WARNING **: 16:39:35.917: cannot open display: 
1/1 gnome-software / gs-self-test-core FAIL 0.04 s (exit status 1)

OK: 0
FAIL: 1
SKIP: 0
TIMEOUT: 0

ERROR: Job failed: exit code 1