Core/Units: CanFly and CanHover will now return positive results when the creature has the according movement flags dispite not having the template movement field set as enabled. This fixes several edge cases with manually enabled flight movement

* renamed IsLevitating to IsGravityDisabled for consistency

src/server/game/Entities/Unit/Unit.cpp

@@ -14377,7 +14377,7 @@ bool Unit::SetDisableGravity(bool disable, bool packetOnly /*= false*/)
 {
     if (!packetOnly)
     {
-        if (disable == IsLevitating())
+        if (disable == IsGravityDisabled())
             return false;
 
         if (disable)
@@ -14454,7 +14454,7 @@ bool Unit::SetCanFly(bool enable, bool packetOnly)
         }
         else
         {
-            if (IsFlying() && !IsLevitating())
+            if (IsFlying() && !IsGravityDisabled())
                 SetFall(true);
             RemoveUnitMovementFlag(MOVEMENTFLAG_CAN_FLY | MOVEMENTFLAG_MASK_MOVING_FLY);