window-list: Use consistent style class prefix

This will eventually allow us to re-use the workspace-indicator
extension without changing anything but the used prefix.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell-extensions/-/merge_requests/307>

extensions/window-list/stylesheet-dark.css

@@ -102,12 +102,12 @@
   background-color: #3f3f3f;
 }
 
-.window-list-window-preview {
+.window-list-workspace-indicator-window-preview {
   background-color: #bebebe;
   border-radius: 1px;
 }
 
-.window-list-window-preview.active {
+.window-list-workspace-indicator-window-preview.active {
   background-color: #d4d4d4;
 }
 

extensions/window-list/stylesheet-light.css

@@ -61,11 +61,11 @@
   border-color: #888;
 }
 
-.window-list-window-preview {
+.window-list-workspace-indicator-window-preview {
   background-color: #ededed;
   border: 1px solid #ccc;
 }
 
-.window-list-window-preview.active {
+.window-list-workspace-indicator-window-preview.active {
   background-color: #f6f5f4;
 }

extensions/window-list/workspaceIndicator.js

@@ -27,7 +27,7 @@ class WindowPreview extends St.Button {
 
     constructor(window) {
         super({
-            style_class: 'window-list-window-preview',
+            style_class: 'window-list-workspace-indicator-window-preview',
         });
 
         this._delegate = this;