Rename TrackerHand enums

[madmiraal]

As identified here, the TrackerHand enums are named inconsistently:

godot/servers/xr/xr_positional_tracker.h

Lines 51 to 55 in 2a325f3

	enum TrackerHand {
	TRACKER_HAND_UNKNOWN, /* unknown or not applicable */
	TRACKER_LEFT_HAND, /* controller is the left hand controller */
	TRACKER_RIGHT_HAND /* controller is the right hand controller */
	};

This PR renames:
TRACKER_LEFT_HAND -> TRACKER_HAND_LEFT
TRACKER_RIGHT_HAND -> TRACKER_HAND_RIGHT

Part of #16863

[akien-mga]

Thanks!