[Touch UI] Check when UI gameObject is touched

• Added new script LeanTouchUI.cs to check when UI is touched
• Refactor the method LeanTouch.RaycastGui() that contains an error, and "copied/changed" to LeanTouchUI.Raycast() method. The only part of this method that was changed the layer verification:

// Loop through all results and remove any that don't match the layer mask
if (tempRaycastResults.Count > 0)
{
	for (var i = tempRaycastResults.Count - 1; i >= 0; i--)
	{
		var raycastResult = tempRaycastResults[i];
		var raycastLayer = 1 << raycastResult.gameObject.layer;
		string layerName = LayerMask.LayerToName(raycastResult.gameObject.layer);

		// PS: That was changed from LeanTouch.RaycastGui()
		if (!LayerMask.GetMask(layerName).Equals(raycastLayer))
		{
			tempRaycastResults.RemoveAt(i);
		}
	}
}

TODO

• Check the Github actions workflow that shows a "permission denied" error when try do a push to upm branch.