RFR 8013541: Revise javadoc for Executable.getAnnotatedReturnType()

[Joel Borggrén-Franck]

Hello all,

Also a small update to the javadoc of Executable to make it more consistent 
for type annotations.

http://cr.openjdk.java.net/~jfranck/8013541/webrev.00/

For oracle reviewers, CCC is filed.

cheers
/Joel