Fix Scribe mobile issues

- Fix Scribe replace on mobile when opened from menu bar (to be complete
this fix needs this PR https://github.com/Enough-Software/enough_html_editor/pull/37)
- Ensure all mobile editor call are awaited
- Do not clear text if a selection has been restored (which mean we replace a selection)
- Avoid collapseToEnd crash

core/lib/utils/html/html_utils.dart

@@ -197,7 +197,7 @@ class HtmlUtils {
     script: '''
       (() => {
         const selection = window.getSelection();
-        if (selection) {
+        if (selection && selection.rangeCount > 0) {
           selection.collapseToEnd()
         }
       })();''',
@@ -220,9 +220,10 @@ class HtmlUtils {
         const selection = window.getSelection();
         if (selection && selection.rangeCount > 0) {
           window._savedRange = selection.getRangeAt(0).cloneRange();
-          return true;
+          return selection.toString();
         }
-        return false;
+        delete window._savedRange;
+        return "";
       })();''',
     name: 'saveSelection');
 
@@ -234,10 +235,10 @@ class HtmlUtils {
           if (selection) {
             selection.removeAllRanges();
             selection.addRange(window._savedRange);
-            return true;
+            return selection.toString();
           }
         }
-        return false;
+        return "";
       })();''',
     name: 'restoreSelection');