[mlir][polynomial] implement add for polynomial data structure (#92169)

A change extracted from https://github.com/llvm/llvm-project/pull/91655,
where I'm still trying to get the attributes working

[mlir][polynomial] implement add for polynomial data structure (#92169)

A change extracted from https://github.com/llvm/llvm-project/pull/91655,
where I'm still trying to get the attributes working for elementwise
constant folding of polynomial ops. This piece is self-contained.

- use CRTP for base classes
- Add unit test

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Co-authored-by: Jeremy Kun <j2kun@users.noreply.github.com>

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