Rebase on fd.o platform instead of GNOME one #219

Problem

The GNOME platform 49 has a regression that the cursor gets big in the app windows with Mutter we ship on OS 8.x:

#215 (comment)
elementary/gala#2683

Proposal

Give a shot if we should build our flatpak platform on the freedesktop platform directly instead of the GNOME one.

• Create a test branch that based on fd.o runtime and uses newer vessels of GTK, libadwaita, etc. in the flatpak-platform repo (maybe version 9 because it’s a breaking change): Rebase on freedesktop platform #220
• Build and install it locally
• Check if all flatpak manifests we maintain build succeed locally and the cursor issue is fixed after switching the based runtime to it
  • browser
  • calculator
  • calendar
  • camera
  • capnet-assist
  • code
  • contacts
  • evince
  • fileroller
  • font-viewer
  • iconbrowser
  • mail
  • maps
  • music
  • papers
  • photos
  • screenshot
  • tasks
  • videos
• Merge the change into the flatpak-platform repo

Prior Art (Optional)

No response