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()`

docs/panel-surfaces.md

@@ -101,7 +101,11 @@ Escape, bound and disposed with `bindPanelDisclosure` /
 `collapsePanelOnEscape` from `panelDisclosure.js` (which bind Escape only). Do not rerun the whole application chrome
 initializer just to add one panel. `layoutLeftPanelRail` and
 `layoutRightPanelRail` accept arbitrary direct `data-panel-id` children; their
-host owns layout scheduling, observations and collapse callbacks. Dynamic
+host owns layout scheduling, observations and collapse callbacks. A rail
+never writes a panel's classes: it calls `onCollapse(panel, {collapsed,
+auto})`, and the host draws that state (the application presents it to the
+panel chrome store, which each root's `v-panel-state` draws at once, so the
+rail can measure the panel in the same task). Dynamic
 content that changes size may require an owner-scheduled layout pass or an
 owned `ResizeObserver`; adding CSS attributes does not register new observers.