The arith dialect provides a big menu of casting/conversion operations
that we can use but which have their own rules and semantics. For
example, the generation of a quantum circuit can involve aggressive
constant propagation. By using an operation in a dialect we control
(CC), we can implement folding and combing these operations in ways that
are suitable to our domain and do not rely on decisions in the MLIR code
that may be too conservative or too aggressive for our needs.

[core] Add constant folding of cc.cast operations.

These constant folding operations will eliminate cc.cast operations when
they are converting the type of a constant input op.

Update the tests.

Add pattern to eliminate integer casts into an integer comparison.

Add constant folding of complex.create. Apparently MLIR doesn't do this.

Add cast complex to complex and various constant foldings.

Add a new test.

Add codegen expansion pattern.