Draft: (After 3.0) Issue #1261: Restore GUI to Difference Clouds script
This patch attempts to resolve #1261.
Difference Clouds displayed a GUI in GIMP 2.8, which came from the Solid Noise plug-in. When Solid Noise was converted to a GEGL operation, it no longer showed a GUI when called from a script.
This patch adds custom parameters to the Difference Cloud so that it will auto-generate a GUI, restoring the ability to configure most settings for Solid Noise. Because of commit f92f7d42, script-writers can still call Difference Clouds without the new parameters to retain the GIMP 2.10 behavior.
I tried to match the GIMP 2.8 Solid Noise dialogue with the dialogue layout, though I'm happy to re-arrange if preferred (within the limits of the Script-fu auto-generated GUI layouts)
EDIT: Per @ajonsson, only strings translated for other Script-fu are available, so we can't merge without either breaking string freeze or showing an untranslated dialogue.