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.

docs/VUE-MIGRATION.md

@@ -67,7 +67,13 @@ a feature supplying only its accent.
    mirrors each side's panels and the rail renders from it. Each panel's
    collapse button (`PanelCollapseButton`), the dock tray toggles and the
    dock pins render the open and pinned state PanelChrome presents to the
-   `gev-panel-chrome` store, and their clicks call it there. Done.
+   `gev-panel-chrome` store, and their clicks call it there. Each panel's
+   root draws its own state from there too (`v-panel-state`: `collapsed`,
+   `dock-pinned`, `dock-pinned-top`, `layout-auto-collapsed`,
+   `accordion-collapsed`): PanelChrome, the rails and the accordion present
+   it rather than writing classes. The directive applies it in a synchronous
+   watcher, not on Vue's next render, because the rails measure a panel in
+   the same task that opens or closes it. Done.
 3. **Panels.** Each template and its wiring become a component, keeping ids,
    classes, `data-i18n` text and CSS. The page places each view with a
    `.gev-view` host (`display: contents`), and `mountApplicationViews()`