[JS] Use beforeinput event to trigger a keystroke event in the sandbox

- it aims to fix issue #14307;
 - this event has been added recently in Firefox and we can now use it;
 - fix few bugs in aform.js or in annotation_layer.js;
 - add some integration tests to test keystroke events (see `AFSpecial_Keystroke`);
 - make dispatchEvent in the quickjs sandbox async.

src/scripting_api/event.js

@@ -151,6 +151,14 @@ class EventDispatcher {
           value: savedChange.value,
           selRange: [savedChange.selStart, savedChange.selEnd],
         });
+      } else {
+        // Entry is not valid (rc == false) and it's a commit
+        // so just clear the field.
+        source.obj._send({
+          id: source.obj._id,
+          value: "",
+          selRange: [0, 0],
+        });
       }
     }
   }