Relax Broadcastable trait to only reject instances that are statically incompatible

Currently, Broadcastable trait also rejects instances when the op result has shape other than what can be statically inferred based on the operand shapes even if the result shape is compatible with the inferred broadcasted shape.

For example,
(tensor<3x2xi32>, tensor<*xi32>) -> tensor<4x3x2xi32>
(tensor<2xi32>, tensor<2xi32>) -> tensor<*xi32>

PiperOrigin-RevId: 258647493