[Grappler] Fold multiply into the weights of a convolution.

This is beneficial when the weights are constant so the multiply can be folded.
For example,

         Conv2D
        /      \
    Transpose  weights
       |
      Mul
     /   \
   inputs 255.0

          ||
          \/

         Conv2D
        /      \
    Transpose   Mul
       |       /   \
       |   weights  255.0
       |
     inputs

PiperOrigin-RevId: 170747451