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/testSupport/panelState.mjs

@@ -0,0 +1,21 @@
+// src/testSupport/panelState.mjs — present a panel's state the way the shell
+// does (PanelChrome._presentPanel), drawn at once as its root's v-panel-state
+// would, for fixtures whose panels are plain objects with a classList.
+import { applyPanelState, readPanelState } from '../ui/rail/panelState.js';
+
+/**
+ * @param {object|string} panelOrId A panel, or its id in `documentRef`.
+ * @param {object} [patch] The state that changes.
+ * @param {Document} [documentRef]
+ */
+export function presentPanelLocally(
+  panelOrId,
+  patch = {},
+  documentRef = globalThis.document,
+) {
+  const panel =
+    typeof panelOrId === 'string'
+      ? documentRef?.getElementById(panelOrId)
+      : panelOrId;
+  if (panel) applyPanelState(panel, { ...readPanelState(panel), ...patch });
+}