[Lynx] Workaround in the GestureManager to detect system gestures

[javifernandez]

Since Lynx 1.1.8 we can really on the XR_FB_hand_tracking_aim OpenXR Extension, so we can use the its specific Gesture Manager. It works fine for the getting poses and managing pinching gestures, but the XR_HAND_TRACKING_AIM_SYSTEM_GESTURE_BIT_FB is not properly set, so we can not use it to detect system gestures. Hence, we need to rely on the GestureManager implementation based on the manual computation of the hand's position and orientation.

Additionally, the XR_HAND_TRACKING_AIM_VALID_BIT_FB is not being updated either, so we can't rely on it to be sure the hand gesture is actually meant to be a system gesture.

Fixes #1392

[svillar]

I'd also suggest to change a bit the title to something like [Lynx] Use XR_FB_hand_tracking_aim extension ?

[javifernandez]

I'd also suggest to change a bit the title to something like [Lynx] Use XR_FB_hand_tracking_aim extension ?

Umm, I think that the relation between that title and the code change isn't obvious. As a matter of fact, we were using the extension with upgrading the SO to the version 1.1.8. The PR is more about fixing a bug when using the extension.