As described in http://cr.openjdk.java.net/~briangoetz/amber/constables.html, provide a family of types to model nominal descriptions of classes, method handles, and other runtime or classfile entities, and retrofit them into core classes such as String and Class.  These will live in the new package `java.lang.invoke.constant`.  

This issue tracks the base abstractions `ConstantDesc` and `Constable`, and their subtypes.  Bytecode APIs and bootstrap methods can use `ConstantDesc` to describe constants; compilers can use `Constable` as part of intrinsification and constant folding.  Compiler and language support is part of a separate task.