FP8 Convolutions in XLA
CC @reedwm, @nluehr. Can you resolve conflicts?
Enables scaled convolutions of the form

(X, W, x_scale, w_scale, y_scale) -> Y,

where the input X, the filter W and the output Y are based on the `F8E4M3FN` and `F8E5M2` data types and x_scale, w_scale and y_scale are their scaling factors.