[Editor] Dispatch an event when some global states are changing

- this way the context menu in Firefox can take into account what we
  have in the clipboard, if an editor is selected, ...
- when the user will click on a context menu item, an action will be
  triggered, hence this patch adds what is required to handle it;
- some tests will be added in the Firefox' patch.

web/firefoxcom.js

@@ -271,6 +271,20 @@ class MozL10n {
   window.addEventListener("save", handleEvent);
 })();
 
+(function listenEditingEvent() {
+  const handleEvent = function ({ detail }) {
+    if (!PDFViewerApplication.initialized) {
+      return;
+    }
+    PDFViewerApplication.eventBus.dispatch("editingaction", {
+      source: window,
+      name: detail.name,
+    });
+  };
+
+  window.addEventListener("editingaction", handleEvent);
+})();
+
 class FirefoxComDataRangeTransport extends PDFDataRangeTransport {
   requestDataRange(begin, end) {
     FirefoxCom.request("requestDataRange", { begin, end });
@@ -384,6 +398,10 @@ class FirefoxExternalServices extends DefaultExternalServices {
     return new FirefoxPreferences();
   }
 
+  static updateEditorStates(data) {
+    FirefoxCom.request("updateEditorStates", data);
+  }
+
   static createL10n(options) {
     const mozL10n = document.mozL10n;
     // TODO refactor mozL10n.setExternalLocalizerServices