Legalizes frozen TF ops to to StableHLO before running quantization passes.
Legalizes frozen TF ops to to StableHLO before running quantization passes.

After variable freezing, there will be `tf.Const`->`tf.Cast` patterns remaining in the graph. To convert these to `stablehlo.constant`s, TF->StableHLO legalization is required.
A `TFShapeInferencePass` is also required before running the legalization passes to resolve unknown shapes after variable freezing.
