Issue #4922: install software-update-available from Adwaita on hicolor.

I took the icon directly from Adwaita repository as of today's version:
https://gitlab.gnome.org/GNOME/adwaita-icon-theme/-/blob/master/Adwaita/scalable/status/software-update-available-symbolic.svg

By being installed on our local GIMP-only hicolor, this gets picked up
after any custom theme software-update-available version. I didn't
install it inside the Symbolic or Color theme because anyway Adwaita
seems only to provide a single vector version. There is a color version,
yet as PNG icons and installed in the legacy/ section. I don't think it
makes sense to use an icon considered as legacy by its author and
without vector version. So I just install the symbolic version and all
themes can fallback to it (be them symbolic icon themes or not).

This icon comes from the Adwaita repository and is therefore licensed
under the terms of either the GNU LGPL v3 or Creative Commons
Attribution-Share Alike 3.0 United States License. See:
https://gitlab.gnome.org/GNOME/adwaita-icon-theme/-/blob/master/COPYING

icons/hicolor/Makefile.am

@@ -4,9 +4,14 @@ icons_DATA = \
 
 actionsdir = $(iconsdir)/scalable/actions
 actions_DATA = \
-	scalable/switch-on-symbolic.svg		\
-	scalable/switch-off-symbolic.svg
+	scalable/actions/switch-on-symbolic.svg		\
+	scalable/actions/switch-off-symbolic.svg
+
+statusdir = $(iconsdir)/scalable/status
+status_DATA = \
+	scalable/status/software-update-available-symbolic.svg
 
 EXTRA_DIST = \
 	$(icons_DATA)		\
-	$(actions_DATA)
+	$(actions_DATA)		\
+	$(status_DATA)

icons/hicolor/index.theme

@@ -3,7 +3,7 @@ Name=Hicolor
 Comment=Fallback icon theme
 Hidden=true
 
-Directories=scalable/actions
+Directories=scalable/actions,scalable/status
 
 [scalable/actions]
 Context=Actions
@@ -11,3 +11,10 @@ Size=16
 MinSize=8
 MaxSize=512
 Type=Scalable
+
+[scalable/status]
+Context=Status
+Size=16
+MinSize=8
+MaxSize=512
+Type=Scalable

icons/hicolor/meson.build

@@ -3,8 +3,9 @@ install_data('index.theme',
 )
 
 generic_icons = [
-  [ 'scalable/actions/', 'scalable/switch-on-symbolic.svg' ],
-  [ 'scalable/actions/', 'scalable/switch-off-symbolic.svg' ]
+  [ 'scalable/actions/', 'scalable/actions/switch-on-symbolic.svg' ],
+  [ 'scalable/actions/', 'scalable/actions/switch-off-symbolic.svg' ],
+  [ 'scalable/status/',  'scalable/status/software-update-available-symbolic.svg' ]
 ]
 
 foreach icon_info : generic_icons

icons/hicolor/scalable/status/software-update-available-symbolic.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16"><path d="M8 .063L5.75 3.469 2.312 2.313 3.47 5.75.063 8l3.406 2.25-1.156 3.438L5.75 12.53 8 15.937l2.25-3.406 3.438 1.156-1.157-3.437L15.937 8l-3.406-2.25 1.156-3.438L10.25 3.47zm0 4.53l.719.688 2 2c.223.226.331.561.281.875V9h-.875a1.032 1.032 0 01-.844-.281L9 8.437V11H7V8.437l-.281.282A1.036 1.036 0 016 9H5v-.781a1.465 1.465 0 010-.094c-.04-.304.067-.624.281-.844l2-2z" fill="#474747" fill-rule="evenodd"/></svg>