[XLA] Additional fp8 matmul patterns
@reedwm This PR is essential to test performance on GPT transformer models. Hi @wenscarl Can you please check @reedwm's comments and resolve conflicts?. Thank you! I think https://github.com/tensorflow/tensorflow/pull/59971 replaces this PR, so closing this PR.
This PR extends currently supported patterns,
matmul <- bitcast <- multiply and matmul <- multiply to

matmul <- bitcast <- copy <- bitcast <- multiply
matmul <- bitcast <- copy <- multiply
matmul <- bitcast <- copy <- reshape <- multiply
matmul <- copy <- bitcast <- multiply