Review request: JDK-8211122: Reduce the number of internal classes made accessible to jdk.unsupported

[Mandy Chung]

This patch includes the following changes that will reduce the
number of internal classes made accessible to jdk.unsupported
module via qualified exports.

1. move shared secrets to a new jdk.internal.access package.

jdk.internal.misc package has been a dumping ground for various
kinds of internal APIs and many of which were moved to an appropriate
package. This is a follow-up clean up that moves the shared secrets
and JavaXXXAccess interfaces to jdk.internal.access package.

2. add a wrapper class jdk.internal.misc.FileSystemOption to expose
sun.nio.fs.ExtendedOptions for com.sun.nio.file to access

This eliminates the qualified exports of sun.nio.fs to jdk.unsupported.

3. Refactor the implementation of sun.misc.Unsafe::invokeCleaner
to jdk.internal.misc.Unsafe.

This eliminates the qualified exports of jdk.internal.ref and
sun.nio.ch to jdk.unsupported.

Webrev:
http://cr.openjdk.java.net/~mchung/jdk12/webrevs/8211122/webrev.02

The change is straight forward although quite many files are modified.
Majority of the changes is import statement change or test @modules
change due to the rename.

I ran hs-tier1-3 and jdk-tier1-3 tests.

We considered the alternative to define a wrapper class for everything
that jdk.unsupported module depends on in a dedicated package
e.g. jdk.internal.unsupported.  It would need a wrapper for Unsafe,
Signal, SignalHandler and ExtendedOptions.  It means that it would
have 3 classes of each - two similar/duplicated implementations
(one in sun.misc and one in jdk.internal.unsupported) and one
in jdk.internal.misc ([1] is the prototype).  Only a limited number
of files are touched but I think the proposed approach is cleaner.

Thanks
Mandy
[1] http://cr.openjdk.java.net/~mchung/jdk12/webrevs/8211122/webrev.01/