New JEP: Javac intrinsics for LDC and INVOKEDYNAMIC

[Brian Goetz]

Please review the this JEP draft:

     https://bugs.openjdk.java.net/browse/JDK-8178320

This JEP creates (a) an official set of purely-nominal wrapper classes for linkable constants (Class, MethodType, MethodHandle, VarHandle), provides constant-propagation (not folding) support in javac for these types, and (b) intrinsification for LDC and INVOKEDYNAMIC so that they can be predictably translated into bytecode.

This allows Java source code to be a first-class client of invokedynamic, including using Java to test indy bootstraps.