refactor(panels): read panel state from the panel chrome store

PanelChrome, its collapse-preference restore and the phone shell read a
panel's disclosure state back from the gev-panel-chrome store
(_shownPanel), falling back to the markup's classes before the panel is
first presented, instead of reading the classes v-panel-state draws. The
share link and the phone shell share one rule for a panel the person keeps
closed (prefersCollapsed). The rails, the accordion and the hover
disclosure still read the classes, which the directive draws in the same
task as their layout.

src/ui/applicationShell.js

@@ -858,6 +858,7 @@ export class StyleManager extends ShellFacade {
     this._mobileShell = initMobileShell({
       setPanelCollapsed: (panelId, collapsed, options) =>
         this._panelChrome.setPanelCollapsed(panelId, collapsed, options),
+      readPanel: (panel) => this._panelChrome._shownPanel(panel),
       onSheetsClosed: () => this._syncShareState(),
       onTabOpened: (sheet) => {
         void this._onMobileTabOpened(sheet);