FIX Allow wrapping an image in a link (#2883)

Relies on logic added to silverstripe/admin, so we need to bump the
constraint as well.

Behat test requires new logic added to the behat-extension module.

client/src/legacy/TinyMCE_sslink-anchor.js

@@ -74,10 +74,7 @@ jQuery.entwine('ss', ($) => {
       const handleHide = () => this.close();
       const handleInsert = (...args) => this.handleInsert(...args);
       const attrs = this.getOriginalAttributes();
-      const selection = tinymce.activeEditor.selection;
-      const selectionContent = selection.getContent() || '';
-      const tagName = selection.getNode().tagName;
-      const requireLinkText = tagName !== 'A' && selectionContent.trim() === '';
+      const requireLinkText = this.getRequireLinkText();
       const currentPageID = Number($('#Form_EditForm_ID').val() || 0);
 
       // create/update the react component

client/src/legacy/TinyMCE_sslink-internal.js

@@ -89,20 +89,6 @@ jQuery.entwine('ss', ($) => {
       );
     },
 
-    /**
-     * Determine whether to show the link text field
-     *
-     * @return {Boolean}
-     */
-    getRequireLinkText() {
-      const selection = this.getElement().getEditor().getInstance().selection;
-      const selectionContent = selection.getContent() || '';
-      const tagName = selection.getNode().tagName;
-      const requireLinkText = tagName !== 'A' && selectionContent.trim() === '';
-
-      return requireLinkText;
-    },
-
     /**
      * @param {Object} data - Posted data
      * @return {Object}

composer.json

@@ -19,7 +19,7 @@
         }
     ],
     "require": {
-        "silverstripe/admin": "^1.12@dev",
+        "silverstripe/admin": "^1.13@dev",
         "silverstripe/campaign-admin": "^1.7@dev",
         "silverstripe/framework": "^4.11",
         "silverstripe/reports": "^4.7@dev",
@@ -55,4 +55,4 @@
     },
     "prefer-stable": true,
     "minimum-stability": "dev"
-}
+}