Adding optional tabindex attr to simple, framed and cm engines (#3756)

* add optional tabindex attribute to factory.js

* add changedAttributes.tabindex to refresh mechanic

* add optional tabindex attribute to edit widget

* remove some extra whitespace

* remove some trailing whitespace

* add optional tabindex attribute to simple engine

* add optional tabindex attribute to framed engine

* add optional tabindex attribute to cm engine

core/modules/editor/engines/framed.js

@@ -70,6 +70,9 @@ function FramedEngine(options) {
 	if(this.widget.editRows) {
 		this.domNode.setAttribute("rows",this.widget.editRows);
 	}
+	if(this.widget.editTabIndex) {
+		this.iframeNode.setAttribute("tabindex",this.widget.editTabIndex);
+	}
 	// Copy the styles from the dummy textarea
 	this.copyStyles();
 	// Add event listeners

core/modules/editor/engines/simple.js

@@ -49,6 +49,9 @@ function SimpleEngine(options) {
 	if(this.widget.editClass) {
 		this.domNode.className = this.widget.editClass;
 	}
+	if(this.widget.editTabIndex) {
+		this.domNode.setAttribute("tabindex",this.widget.editTabIndex);
+	}
 	// Add an input event handler
 	$tw.utils.addEventListeners(this.domNode,[
 		{name: "focus", handlerObject: this, handlerMethod: "handleFocusEvent"},