RFR: 8234089: (zipfs) Remove classes JarFileSystemProvider and JarFileSystem

[Langer, Christoph]

Hi,

can I please get reviews for this cleanup change in zipfs.

Bug: https://bugs.openjdk.java.net/browse/JDK-8234089
Webrev: http://cr.openjdk.java.net/~clanger/webrevs/8234089.0/

I figured that JarFileSystemProvider is completely obsolete (please correct me if I'm wrong) and the reasons for having a class JarFileSystem that extends ZipFileSystems are very little in my opinion. I think maintainability is better when the few implementation details of multi release jars live in ZipFileSystem as well. It saves some code. The only possible drawback is that ZipFileSystem:: getInode would have an additional call to a lookup function, that usually is an identity transformation. I would hope however, that runtime impact is negligible.

I also fix a small bug when property "releaseVersion" is set to null in the env map and multi-release contains a value. In the current implementation it would not consider the "multi-release" value and treat the mr jar as the current runtime version. I had to do a small fix in MultiReleaseJarTest.java to make sure the properties list is cleared in every case.

The jdk/nio/zipfs tests run well after my change.

Thanks
Christoph