RFR 8197954 Remove unnecessary intermediary APIs from AppCDS implementation

[Ioi Lam]

https://bugs.openjdk.java.net/browse/JDK-8197954
http://cr.openjdk.java.net/~iklam/jdk11/8197954-remove-unnecessary-appcds-api.v01/

Summary:

Before AppCDS was open sourced, we had a few "Ext" classes in 
sharedClassUtil.hpp
that abstracted away the CDS operations related to the non-boot class 
loaders.
This API made it possible to build the Oracle JDK with AppCDS included, 
or build
the Open JDK with AppCDS removed.

With the open sourcing of AppCDS, this abstraction layer is no longer 
necessary. I
have moved the contents of the "Ext" classes into their proper locations 
and removed
the sharedClassUtil.hpp/cpp files.

Most of the changes are just moving things around. There shouldn't be 
behavioral
changes.

The files classLoaderExt.hpp/cpp still exists -- it encapsulates the 
classpath
management code and is not strictly unnecessary. Some clean up may be 
needed there, but
I'll probably do that in a separate RFE.

Testing with hotspot tiers1~4.

Thanks
- Ioi