Add a dropReturn MethodHandle combinator

Summary

Add a dropReturn method handle combinator, that can be used to drop the return value of a method handle.

Problem

There are currently several methods in j.l.i.MethodHandles for dropping arguments, but a similar combinator does not exist for dropping return values. Instead other means such as using a combination of filterReturn and empty, or asType with a void return type have to be used to create a method handle that discards the return value.

Solution

Provide a dropReturn method handle combinator that takes a MethodHandle, and returns a new MethodHandle that is the same as the given method handle, but which discards it's return value.

Specification

/**
 * Drop the return value of the target handle (if any).
 * The returned method handle will have a {@code void} return type.
 *
 * @param target the method handle to adapt
 * @return a possibly adapted method handle
 * @throws NullPointerException if {@code target} is null
 * @since 16
 */
public static MethodHandle dropReturn(MethodHandle target) {
    ...
}