feat(globe): answer the clear and share actions through the globe actions store

The top-center bar is now GlobeActions.vue. The shell publishes whether a
clear is under way and answers the clear and share buttons through the
globe actions store, instead of binding listeners and writing attributes on
the buttons. A shell disposed mid-clear resets the busy state, so the next
shell's bar is not left busy. bindClearLayersControl stays exported and is
deprecated.

src/ui/clearLayersControl.js

@@ -1,6 +1,12 @@
 import { t } from '../i18n/index.js';
 
-/** Keep the clear action focusable while busy; the caller owns its transaction. */
+/**
+ * Keep the clear action focusable while busy; the caller owns its
+ * transaction. The globe actions view renders the button from the globe
+ * actions store now; this stays exported from `./ui/layers` for hosts that
+ * imported it.
+ * @deprecated
+ */
 export function bindClearLayersControl(button, clear) {
   let destroyed = false;
   const click = () => {