Proposal to move src.zip and jrt-fs.zip to the `lib` directory in the run-time image

[Mandy Chung]

Several files in a runtime image are intended for external uses
and their pathname is a committed interface, including:

  jrt-fs.jar 
  src.zip 
  lib/javafx-swt.jar 
  lib/ant-javafx.jar 

The `lib` directory in the runtime image currently defined in 
JEP 220 is private implementation and for internal use only. 
In addition to the above files, external launchers depend on
the path `lib/$VMTYPE/libjvm.so` (or the equivalent) and tools
depend on `lib/jexec`.

The proposal is to redefine the purpose of the `lib` directory.
The `lib` directory will contain read-only files that are 
intended for external use and thus are committed interfaces.

Therefore we propose to move `jrt-fs.jar` and `src.zip` from
the top level into the `lib` directory.  We’ll leave `javafx-swt.jar`
and `ant-javafx.jar` in the `lib` directory.

For the internal files under the `lib` directory, we propose to
leave them in the `lib` directory in JDK 9 and be moved out of 
the `lib` directory in future releases.

This change [1] will impact external tools depending on jrt-fs.jar
and src.zip.  One tentative plan is to make this change in 2 weeks
(possibly jdk-9+147) unless any one needs more time. 

Comments?

Mandy
[1] https://bugs.openjdk.java.net/browse/JDK-8169816