Review Request JDK-8228336: Refactor native library loading implementation

[Mandy Chung]

This patch refactors the native library loading implementation out of 
ClassLoader and move them to jdk.internal.loader package. This 
introduces a new NativeLibraries abstraction which loads and registers 
the loaded native libraries.  Previously it was maintained in a 
nativeLibrary map in each ClassLoader instance and one 
systemNativeLibraries for the null loader case.  With this change, each 
ClassLoader and BootLoader have its own NativeLibraries instead.

NativeLibraries.java and NativeLibraries.c are mostly refactored from 
the existing code.  Only minor cleanups are applied.

This refactoring enables Panama LookupLibrary to further experiment and 
allow loading of a native library without the restriction that a native 
library can only be loaded by one class loader.  The restriction is 
important for System::loadLibrary in loading JNI libraries that 
implements JNI native methods and so remain unchanged.

This patch follows up the change introduced by JDK-8227587 which adds 
BootLoader::loadLibrary.  It should belong a helper classes instead of 
BootLoader and this helper method is to avoid doPrivileged call if no 
security manager is installed for startup performance improvement.   
Several `privilegedXXX` methods were added for the same purpose for 
example sun.security.action.GetPropertyAction::privilegedGetProperty and 
privilegedGetProperties.  So I think 
sun.security.action.LoadLibraryAction is a proper place.

Webrev:
http://cr.openjdk.java.net/~mchung/jdk15/webrevs/8228336/webrev.00/

Thanks
Mandy