[Moore] Add constant materialization, fold constant conversions

[fabianschuiki]

Implement the materializeConstant function for the Moore dialect and mark the ConstantOp as a ConstantLike operation. This now allows us to write constant folders for various operations. As a first example, add a constant folder for ConversionOp that directly applies domain conversions (e.g., i42 to l42 or vice versa) to constants.

[maerhart]

Isn't it required to implement a fold function for operations that have the ConstantLike trait that just returns the attribute?

Also, ConstantStringOp already has ConstantLike added, so maybe also support that in the constant materializer?

Otherwise, this looks great! 🎉

[fabianschuiki]

Oh good point, I forgot about the string constant op. Will add a fold method there. Apparently it's not technically required, or at least nothing complained so far about the string constant being ConstantLike but having no folder. Let me fix that.

[fabianschuiki]

Ugh just realized that the moore.string_constant op returns an IntType, so the folder and constant materializer will have to convert the string constants to an FVInt and back. That's probably something for a separate PR.

[maerhart]

Ugh just realized that the moore.string_constant op returns an IntType, so the folder and constant materializer will have to convert the string constants to an FVInt and back. That's probably something for a separate PR.

Oh, yeah that sounds annoying.

[hailongSun2000]

Awesome！