Plugins: GUI: Move HelloWorld and Sphere plugin menu items to Demos menu.

The "Sphere" plugin demonstrate all the widgets for arguments of a plugin.
Only its menu label is translated.

The "Hello World" plugin demonstrates an independently interpreted SF plugin.
It has no translations, even of its menu label.

Formerly in ..ScriptFu>Test menu.

They still are installed even in a stable release.
If we don't want 3.0 stable to ship with demos,
need more changes to meson.build.

They are akin to the goat exercise plugins.
These plugins are expected to ship with the goat plugins in a stable build.
!!! But 2.10 did not ship with any demo plugins in stable build.

There are duplicate "Sphere" (v2) and "Sphere v3" plugins.

Does not break string freeze.

The new-style "Sphere v3" plugin moves to Demos.
It will be installed with stable build.
No translations will change.

"Sphere" (v2) will only be installed in an unstable build.

FUTURE: we should translate Hello World and Sphere v3.
If they are to ship as demos, their GUI should be translated.

FUTURE: low priority we could rename "Sphere v3" to just Sphere,
and Sphere to "Sphere v2" so there is no conflict.

plug-ins/script-fu/scripts/meson.build

@@ -68,6 +68,9 @@ install_data(
 # Like other interpreted plugins.
 # Lacking a shebang, a .interp file is needed to associate .scm suffix
 
+# !!! These are demo plugins.
+# Install with a stable release along with goat exercise demos.
+
 scripts_independent = [
   { 'name': 'ts-helloworld' },
   { 'name': 'test-sphere-v3' },

plug-ins/script-fu/scripts/test-sphere-v3.scm

@@ -183,4 +183,4 @@
 )
 
 (script-fu-menu-register "script-fu-test-sphere-v3"
-                         "<Image>/Filters/Development/Script-Fu/Test")
+                         "<Image>/Filters/Development/Demos")

plug-ins/script-fu/scripts/ts-helloworld.scm

@@ -64,4 +64,4 @@
 )
 
 (script-fu-menu-register "script-fu-helloworld"
-                         "<Image>/Filters/Development/Script-Fu/Test")
+                         "<Image>/Filters/Development/Demos")