Set height to 100% for text and richtext

Closes #13058

sao/src/sao.less

@@ -783,8 +783,8 @@ img.icon {
     }
     .form-text, .form-richtext {
         > textarea, .richtext {
+            height: 100%;
             line-height: 2.5ex;
-            max-height: 50ex;
             min-height: 12.5ex;
             overflow: auto;
             resize: vertical;