[NVIDIA XLA] Cover D_amax output fusion for FP8 GEMM when Relu is present in epilogue
@reedwm could you take a look? > Please add a test.
> 
> Also maybe move the amax logic to a new function

The following "changing data type of C to BF16" part is also in the body of F8ConvertD.
In the presence of a ReLU activation, algsimp pass simplifies the possible abs op following ReLU, like abs(Relu(x)) -> Relu(x). This PR covers that corner case by adding possible patterns to match.