MethodName is a type of Value that may be
used in an Operand to an Instruction. It references
a MethodSignature.
The MethodName may be constructed either directly or through the Allocator object. It requires that
a MethodSignature be constructed first.
MethodName(MethodSignature *M);
It is possible to retrieve the MethodSignature.
MethodSignature
*Signature() const { return signature_; }