Release Note: JEP 334: JVM Constants API

The new package `java.lang.invoke.constant` introduces an API to model nominal descriptions of class file and run-time artifacts, in particular constants that are loadable from the constant pool. It does so by defining a family of value-based symbolic reference (JVMS 5.1) types, capable of describing each kind of loadable constant. A symbolic reference describes a loadable constant in purely nominal form, separate from class loading or accessibility context. Some classes can act as their own symbolic references (e.g., `String`); for linkable constants a family of symbolic reference types has been added (`ClassDesc`, `MethodTypeDesc`, `MethodHandleDesc`, and `DynamicConstantDesc`) that contain the nominal information to describe these constants.