Open source two simplical attention kernels (#4445)

Summary:

X-link: facebookresearch/FBGEMM#1508

Kernels for two simplical attention of form:
L = Q @ (K1 X K2)
P = softmax(L, axis=[-1, -2])
O = P @ (V1 X V2)

Differential Revision: D77756574

Author: choutim