Add support for generating operation interfaces from the ODS framework.

Operation interfaces generally require a bit of boilerplate code to connect all of the pieces together. This cl introduces mechanisms in the ODS to allow for generating operation interfaces via the 'OpInterface' class.

Providing a definition of the `OpInterface` class will auto-generate the c++
classes for the interface. An `OpInterface` includes a name, for the c++ class,
along with a list of interface methods. There are two types of methods that can be used with an interface, `InterfaceMethod` and `StaticInterfaceMethod`. They are both comprised of the same core components, with the distinction that `StaticInterfaceMethod` models a static method on the derived operation.

An `InterfaceMethod` is comprised of the following components:
    * ReturnType
      - A string corresponding to the c++ return type of the method.
    * MethodName
      - A string corresponding to the desired name of the method.
    * Arguments
      - A dag of strings that correspond to a c++ type and variable name
        respectively.
    * MethodBody (Optional)
      - An optional explicit implementation of the interface method.

def MyInterface : OpInterface<"MyInterface"> {
  let methods = [
    // A simple non-static method with no inputs.
    InterfaceMethod<"unsigned", "foo">,

    // A new non-static method accepting an input argument.
    InterfaceMethod<"Value *", "bar", (ins "unsigned":$i)>,

    // Query a static property of the derived operation.
    StaticInterfaceMethod<"unsigned", "fooStatic">,

    // Provide the definition of a static interface method.
    // Note: `ConcreteOp` corresponds to the derived operation typename.
    StaticInterfaceMethod<"Operation *", "create",
      (ins "OpBuilder &":$builder, "Location":$loc), [{
        return builder.create<ConcreteOp>(loc);
    }]>,

    // Provide a definition of the non-static method.
    // Note: `op` corresponds to the derived operation variable.
    InterfaceMethod<"unsigned", "getNumInputsAndOutputs", (ins), [{
      return op.getNumInputs() + op.getNumOutputs();
    }]>,
  ];

PiperOrigin-RevId: 264754898