[FIRRTL] Dedupe should be able to dedupe classes

[mikeurbach]

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The Dedupe pass currently skips over classes: https://github.com/llvm/circt/blob/2d822eabf696378ba14ce4b1a8a703af1e721589/lib/Dialect/FIRRTL/Transforms/Dedup.cpp#L1523-L1535

It should be possible to dedupe classes and object similarly to modules and instances.