data: Rename custom close icon

Resource icons are added to the fallback icon theme, so they won't
get used if a matching icon is found in the configured theme.

That includes fallback names, so Adwaita's "window-close-symbolic"
takes precedence over "window-close-24-symbolic" in hicolor.

Fix this by using a custom name for a custom icon.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1640>

data/gnome-shell-theme.gresource.xml

@@ -20,7 +20,7 @@
     <file alias="icons/scalable/actions/pointer-drag-symbolic.svg">pointer-drag-symbolic.svg</file>
     <file alias="icons/scalable/actions/pointer-primary-click-symbolic.svg">pointer-primary-click-symbolic.svg</file>
     <file alias="icons/scalable/actions/pointer-secondary-click-symbolic.svg">pointer-secondary-click-symbolic.svg</file>
-    <file alias="icons/scalable/actions/window-close-24-symbolic.svg">window-close-24-symbolic.svg</file>
+    <file alias="icons/scalable/actions/preview-close-symbolic.svg">window-close-24-symbolic.svg</file>
     <file alias="icons/scalable/status/keyboard-caps-lock-filled-symbolic.svg">keyboard-caps-lock-filled-symbolic.svg</file>
     <file alias="icons/scalable/status/keyboard-enter-symbolic.svg">keyboard-enter-symbolic.svg</file>
     <file alias="icons/scalable/status/keyboard-hide-symbolic.svg">keyboard-hide-symbolic.svg</file>

js/ui/windowPreview.js

@@ -353,7 +353,7 @@ var WindowPreview = GObject.registerClass({
         this._closeButton = new St.Button({
             visible: false,
             style_class: 'window-close',
-            child: new St.Icon({ icon_name: 'window-close-24-symbolic' }),
+            child: new St.Icon({ icon_name: 'preview-close-symbolic' }),
         });
         this._closeButton.add_constraint(new Clutter.BindConstraint({
             source: this._windowContainer,