RFR: 8174222: LambdaMetafactory: validate inputs and improve documentation

[Dan Smith]

http://cr.openjdk.java.net/~dlsmith/8174222/webrev.00/ <http://cr.openjdk.java.net/~dlsmith/8174222/webrev.00/>

Please review this update to java.lang.invoke.LambdaMetafactory. Adds some argument validation with tests; improves documentation; renames some variables.

JBS: https://bugs.openjdk.java.net/browse/JDK-8174222 <https://bugs.openjdk.java.net/browse/JDK-8174222>

—Dan