Cherry-pick patches from upstream for device scale (HiDPI) support

* Cherry-pick patches from upstream for device scale (HiDPI) support
  - image-Use-convolution-filters-for-sample-reconstruct.patch
  - gstate-Respect-device-transform-in-stroke.patch
  - default-context-Inherit-device-scale-in-push_group-s.patch
  - subsurface-Handle-device-scales.patch
  - gstate-Move-device-scale-font-scaling-to-gstate.patch
  - gstate-Handle-device-scale-on-surface-as-source.patch
  - spans-traps-Undo-device-transform-from-source-matrix.patch
  - surface-expose-the-device-scale.patch
  - surface-Opencode-create_similar.patch
  - surface-Merge-scratch-construction-into-_cairo_surfa.patch
  - surface-Inherit-device-scale-in-cairo_surface_create.patch
  - trace-Record-set-device-scale.patch
  - script-Add-support-for-replaying-device-scale.patch
  - Downscaling-requires-pixman-0.30.patch
* Update debian/libcairo2.symbols with added cairo_surface_get_device_scale
* Bump pixman build-dependency to >= 0.30.0