Disable KeyBindingManager on right Alt keydown.

This fixes issue #8666.
@RaymondLim 1 sec is just an estimate. I added these `console.log` statements to the code:

```js
        if (!_altGrDown) {
            if (!_ctrlDown && !_altDown && e.ctrlKey && e.keyIdentifier === "Control") {
                console.log("AltGr event 1 detected");
                _ctrlDown = true;
            } else if (_ctrlDown && !_altDown &&
                        e.altKey && e.ctrlKey && e.keyIdentifier === "Alt") {
                console.log("AltGr event 2 detected");
                _altDown = true;
            } else if (_ctrlDown && _altDown &&
                        e.altKey && e.ctrlKey && e.keyIdentifier === "Control") {
                console.log("AltGr event 3 detected");
                _altGrDown = true;
                _enabled = false;
                $(window).on("keyup", _onCtrlUp);
            } else {
                console.log("AltGr detection reset");
                _ctrlDown = false;
                _altDown = false;
            }
        }
```

In the console, if I press and release `AltGr` I see:

```
AltGr event 1 detected
AltGr event 2 detected
```

If I press and hold `AltGr`, I see all 3 messages:

```
AltGr event 1 detected
AltGr event 2 detected
AltGr event 3 detected
```

But there is a delay (maybe closer to 0.5 sec) between the second and third message. That's why it wasn't working for me -- I wasn't waiting long enough before pressing the alphabet key.

Let me know if this is a FOL or it can and should be fixed.