When generating bytecode based on existing `java.lang.reflect.Method`, there is no way to (easily) retrieve its generic signature.

For example, when generating a compatible method with the Classfile API, one may need to create a `MethodSignature`, which is very hard to do when extracting individual components (type parameters, exceptions, generic parameters & return type). There could be a simple solution, like `MethodSignature.parseFrom(method.getGenericSignature())`, but `getGenericSignature()` is private in `Method`.

It would be helpful to provide public API to access the generic signature of a `Method` as `MethodSignature` and/or `String`.