Common API and TestSuite for `Polynomial`, `MPolynomial`

[mkoeppe]

Is there an existing issue for this?

• I have searched the existing issues for a bug report that matches the one I want to file, without success.

Problem Description

Polynomial and MPolynomial are separate classes with inconvenient differences in supported methods.

Proposed Solution

#35076 introduced an empty common abstract base class CommutativePolynomial.

Next, we can specify the common API by defining abstract methods and providing generic method implementations.

Alternatives Considered

N/A

Additional Information

@tscrim