Bias Fusion for FP8 GEMMs in XLA
CC @reedwm. @philipphack Can you please fix merge conflicts? It looks like you also restored the tests removed in #59515. I didn't look over these very carefully, since I assume they are almost identical to the ones that were removed. Yes, only the contracting dimensions should have changed.
Enables the fusion of the addition of a matrix bias for FP8 GEMMs.