- Breaking change: Remove storagePromptClosed state boolean in favor of

`storagePromptState`; used by `ext-storage.js`
- Fix (regression): Ensure storage dialog will not be blocked because of
    canvas updating done for sake of centering background
- Fix (extensions): Ensure `langReady` changes are available by time prefs
  dialog is closed and that its changes have occurred by time extensions
  have first loaded (`setLang` now returns a Promise rather than `undefined`
  as it waits for extension's `langReady` to resolve); this is also useful
  with `ext-storage.js` so we know that `extensions_loaded` (which
  conditionally updates the canvas based on `storagePromptState`) has seen
  `langReady` and the storage extension hasn't set a `storagePromptState`
  of "waiting"

editor/extensions/ext-storage.js

@@ -47,7 +47,7 @@ export default {
       noStorageOnLoad,
       forceStorage
     } = svgEditor.curConfig;
-    const {storage} = svgEditor;
+    const {storage, updateCanvas} = svgEditor;
 
     function replaceStoragePrompt (val) {
       val = val ? 'storagePrompt=' + val : '';
@@ -255,7 +255,8 @@ export default {
               //   the prompt gives the user the option to store data
               setupBeforeUnloadListener();
 
-              svgEditor.storagePromptClosed = true;
+              svgEditor.storagePromptState = 'closed';
+              updateCanvas(true);
             },
             null,
             null,
@@ -265,6 +266,7 @@ export default {
               tooltip: rememberTooltip
             }
           );
+          svgEditor.storagePromptState = 'waiting';
         } else if (!noStorageOnLoad || forceStorage) {
           setupBeforeUnloadListener();
         }