Set 100% width to input-group of form-text and form-richtext

Otherwise if the widget is not translated, the textarea does not expand.

Closes #13320

sao/src/sao.less

@@ -876,12 +876,16 @@ img.icon {
         }
     }
     .form-text, .form-richtext {
-        textarea, .richtext {
-            height: 100%;
-            line-height: 2.5ex;
-            min-height: 12.5ex;
-            overflow: auto;
-            resize: vertical;
+        .input-group {
+            width: 100%;
+
+            textarea, .richtext {
+                height: 100%;
+                line-height: 2.5ex;
+                min-height: 12.5ex;
+                overflow: auto;
+                resize: vertical;
+            }
         }
     }
     .form-richtext {