Move ringing status indicator to header on mobile

On mobile, the ringing status indicator is supposed to display in the header rather than on a tile. The exact layout differs between Android and iOS. To get it right I had to refactor AppBar to use CSS grid templates.

(Also, I changed my mind about the exact ringing data I needed out of CallViewModel - sorry. A little move of the ringtone audio renderer into its own component was necessary to accommodate that.)

src/components/CallFooterViewModel.tsx

@@ -173,9 +173,7 @@ export function createCallFooterViewModel(
         callModel.setSettingsOpen$,
       ]).pipe(
         map(([isPip, showHeader, setSettingsOpen]) =>
-          !isPip &&
-          !(headerStyle === HeaderStyle.AppBar && showHeader) &&
-          showControls
+          !isPip && headerStyle !== HeaderStyle.AppBar && showControls
             ? (): void => setSettingsOpen(true)
             : undefined,
         ),