[XLA] Enable explicit broadcast for ternary operations.

Also explicitly broadcast constant 1 in algsimp for pow(x, -1) => 1/x transformation, so that:
  - we can avoid implicit broadcast which we are trying to eliminate at HLO level.
  - interpreter, which does not support implicit broadcast, now passes the PowSpecialF32 test case in array_elementwise_ops_test which generates a divide(1.F32[], param.F[4]) instruction that requires implicit broadcast.

PiperOrigin-RevId: 176582286