RFR [9] 8152190: Move sun.misc.JarIndex and InvalidJarIndexException to an internal package

[Chris Hegarty]

sun.misc.JarIndex, and its accompanying InvalidJarIndexException, are not
"Critical APIs", as defined by JEP 260, so they should be moved out of
sun.misc and placed into a more appropriate package where they can
be encapsulated.

http://cr.openjdk.java.net/~chegar/8152190/00/
https://bugs.openjdk.java.net/browse/JDK-8152190

Since the Exception type is only ever statically referenced where it is 
thrown, I’ve moved it to a static nested class of JarIndex, so as to 
keep the namespace cleaner.

-Chris.