(zipfs) Refactoring and cleanups to prepare for JDK-8213031

Before JDK-8213031 is reviewed, there are some refactorings and cleanups that could be separated out. This will keep the actual fix for JDK-8213031 smaller and more concise for reviewing.

Some details:
Improve error handling for ZipFileAttributeView::get methods
improve handling for zip64 attribute/version
minor clenaups such as adding @Override annotations, whitespace fixes, private method visibility etc.
The fix for JDK-8222440 has made some methods and fields from ZipFileSystem non-private to be used by JarFileSystem's new method getNodeInRootTree(). We make these private again and move the getNodeInRootTree logic to ZipFileSystem.