Add contiguous()/try_contiguous() as a method to trait ReshapeTo

[coreylowman]

These two methods can just have default implementations of calling reshape:

fn try_contiguous(self) -> Result<Self, D::Err> {
   self.try_reshape_like(self.shape()) 
}

This works because reshape already ensures that output is contiguous, and calling reshape with the same shape of the tensor will ensure it has the same shape.