[XLA] Also inject reduce-precision instructions inside kInput and kOutput fusion nodes.

The kInput fusion node type has elementwise operations fused into the input side, and the kOutput fusion node type has elementwise operations fused onto the output side.  Thus, we can include those along with kLoop fusion nodes in the reduce-precision-insertion-pass code path that injects the instructions inside the fusion node.

PiperOrigin-RevId: 167628771