style: Improve text scaling support

- new drawing function to convert px to em, for select instances
- updated fontsize function to convert fonts in pt to em
- replace instances of discrete sizes with defined values
- fix instances where assets or icons did not scale along with text
- rework panel buttons to accommodate the scaling padding and icons
- new 'scalable' definitions for elements that follow text scaling

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3033>

js/ui/appDisplay.js

@@ -2607,7 +2607,7 @@ export const AppFolderDialog = GObject.registerClass({
 
         // Edit button
         this._editButton = new St.Button({
-            style_class: 'edit-folder-button',
+            style_class: 'icon-button',
             button_mask: St.ButtonMask.ONE,
             toggle_mode: true,
             reactive: true,