jdk example that uses one module's loader to load a resource file in another module

[Mandy Chung]

I find an example in the jdk that one module (javac) attempts to load a 
resource file in another module (apt) using its module loader.  Since 
apt is not required by javac, it fails to find the apt's resource bundle.

This indicates that there likely exists legacy applications that may do 
the same thing.  It works fine in the legacy app.  When migrating legacy 
apps to modules, the legacy app may require changes like this javac / 
apt case.

Details:

com.sun.tools.javac.util.JavacMessages class is in the javac module 
while it is also used by the apt tool (apt module) for apt diagnostic. 
In com.sun.tools.apt.util.Bark constructor:

        // register additional resource bundle for APT messages.
        JavacMessages aptMessages = JavacMessages.instance(context);
        aptMessages.add("com.sun.tools.apt.resources.apt");
        aptDiags = new JCDiagnostic.Factory(aptMessages, "apt");

The com.sun.tools.javac.util.JavacMessages.getBundles() implementation 
loads a resource bundle with its own class loader (by calling 
java.util.ResourceBundle.getBundle(String).  In the legacy world, it has 
no problem finding "com.sun.tools.apt.resources.apt" resource bundle 
since com.sun.tools.javac.util.JavacMessages class and apt's resource 
files are on the class path.  In the module world, javac and apt are two 
separate modules loaded by two different module loader.   So 
com.sun.tools.javac.util.JavacMessages class fails to find the 
"com.sun.tools.apt.resources.apt" resource bundle that is in the apt module.

As discussed with Jon, to fix this specific javac/apt resource file 
issue, the loader of the apt module should be included as part of the 
apt context when passing to JavacMessages.

Mandy