feat(panels): render each panel's state classes from the store

A panel's collapsed, dock-pinned, dock-pinned-top, layout-auto-collapsed
and accordion-collapsed classes are drawn by its root's v-panel-state from
the gev-panel-chrome store. PanelChrome, its restore, the layout
controller, both rails and the side accordion present each panel's state
there instead of writing its classes; the rails call onCollapse(panel,
{collapsed, auto}). The directive applies a change in a synchronous
watcher, since the rails measure a panel in the task that opens or closes
it.

Destroying the chrome inside Cockpit now puts back the panels Cockpit's
entry closed while it can still present them. Without a shell, the voice
tools' set_panel_open reports that there is no panel to open. QA scripts
present the states they set instead of writing the classes.

src/ui/shellFacade.js

@@ -1024,13 +1024,14 @@ export class ShellFacade {
   }
 
   /**
-   * Updates collapse button glyphs based on panel state. Right-rail panels
-   * use directional arrows; left-stack panels use +/- symbols.
-   * @param {HTMLElement} panelEl - The panel DOM element.
+   * Presents a panel's state, merged over what it shows now; its root and
+   * buttons draw it from the panel chrome store.
+   * @param {HTMLElement|string} panelOrId - The panel or its id.
+   * @param {object} [patch] - The state that changes.
    * @returns {void}
    */
-  _syncPanelCollapseButton(panelEl) {
-    return this._panelChrome._syncPanelCollapseButton(...arguments);
+  _presentPanel(panelOrId, patch) {
+    return this._panelChrome._presentPanel(...arguments);
   }
 
   _buildSharePanelState() {