RFR(M) 8192921 Improve CDS support for custom loaders

[Ioi Lam]

http://cr.openjdk.java.net/~iklam/jdk13/8192921-cds-cust-loader-improve.v01/
https://bugs.openjdk.java.net/browse/JDK-8192921


ISSUE:

In JDK 12, there's experimental support for custom loader in CDS.
However, there are limitations:

1. if two or more custom loaders want to load a class named "A", only
    one of those loaders can actually succeed in loading an archived
    class.

2. the classlist needs to be hand-crafted (or by a script that parses
    the output of -Xlog:class+load=debug).

FIX:

1. Now you can archive multiple classes of the same name. At run
    time, we select an archived class that
    (a) matches the fingerprint of the class file, and
    (b) matches the class hierarchy of the current loader.

    (b) is the tricky part. See
SystemDictionaryShared::has_same_hierarchy_for_unregistered_class

    For a test case, see DuplicatedClassesTest.java

2. -XX:DumpLoadedClassList now automatically includes classes loaded
    by custom loaders. The generated class list includes all the
    necessary attributes for custom loader support, such as "super:",
    "source:" and "interface:".

I have tested with Eclipse IDE, which loads most of its classes with
custom loaders. I am planning to add more test cases.

Thanks
- Ioi