RFR: 8215492: Rename INTERNAL_EMPTY to something less "internal"

[Per Liden]

The INTERNAL_EMPTY macro is sometimes useful outside of access*.[ch]pp. 
We should change the name of that macro and allow it to be used, for 
example, in JNIHandle code, which today passes a "0".

I propose that we change it to DECORATORS_NONE, but I'm open to other 
suggestions.

This patch also adjusts the JNI Handle code to make use of this macros 
instead of using "0".

Bug: https://bugs.openjdk.java.net/browse/JDK-8215492
Webrev: http://cr.openjdk.java.net/~pliden/8215492/webrev.0

(Note! This patch is based on JDK-8215451, which has not yet propagated 
from jdk/jdk12 to jdk/jdk)

/Per