Convert polynomial coefficient type to use modarith

[j2kun]

Major changes in this PR:

• coefficientModulus attribute removed from ring attribute
• coefficientType relaxed to allow AnyType
• polynomial op verifiers enhanced to ensure scalar and polynomial coefficient types agree
• polynomial-to-standard renamed to polynomial-to-mod-arith, and most lowerings emit mod_arith ops
• SubAsAdd canonicalization pattern removed; lowering subtraction directly is more efficient.
• Copied additional upstream polynomial tests that I forgot to in my last PR (e..g, tests/Dialect/Polynomial/IR/errors.mlir)

Shortcomings:

• polynomial-to-mod-arith will fail for basically all polynomial types with non-mod-arith coefficient types. Since we don't have a use case for lowering int/float polynomials, I'm OK with this state of affairs indefinitely.
• The NTT lowering is mostly unchanged, and I just take the mod-arith types, unpack them to their underlying integer type/value, and repack it back up as a mod-arith at the end. I just didn't have it in me to re-write the entire NTT lowering in this already gargantuan PR.

[WoutLegiest]

LGTM, lot is boilerplate changes of types, namespaces and conversion to the new types