Allow global keyboard shortcuts to override all other shortcuts by providing a special field (#6735)

* allow global keyboard shortcuts to override all other shortcuts by providing a special field

* rework the global shortcuts taking priority

* replace bool option with options object in KeyboardManager's keydown handler

* update keyboard shortcut documentation to add information about the new priority setting

* add support for priority global keyboard shortcuts to code mirror

* update the feature's docs to point out it was/will be introduced in 5.2.4

* rollback unnecessary change

core/modules/widgets/keyboard.js

@@ -53,6 +53,10 @@ KeyboardWidget.prototype.render = function(parent,nextSibling) {
 };
 
 KeyboardWidget.prototype.handleChangeEvent = function(event) {
+	if ($tw.keyboardManager.handleKeydownEvent(event, {onlyPriority: true})) {
+		return true;
+	}
+
 	var keyInfo = $tw.keyboardManager.getMatchingKeyDescriptor(event,this.keyInfoArray);
 	if(keyInfo) {
 		var handled = this.invokeActions(this,event);