function createAriaDomNode(parent) {
    if (!parent) {
        if (ariaDomNodeCreated) {
            return;
        }
        ariaDomNodeCreated = true;
    }
    aria.setARIAContainer(parent || mainWindow.document.body);
}
Create ARIA dom node inside parent,
or only for the first editor instantiation inside document.body.
@param parent container element for ARIA dom node