RFR 8157310: jdk.dynalink.linker.support.Lookup should have more checks before adding module read link

[Sundararajan Athijegannathan]

Please review http://cr.openjdk.java.net/~sundar/8157310/ for
https://bugs.openjdk.java.net/browse/JDK-8157310

What is this fix?

* When unreflecting caller sensitive methods, dynalink uses specific
Lookup of actual caller (instead of publicLookup) - in nashorn's case
it's be the Lookup of script class.

* Script class may not have read link to the module of the class (of
caller sensitive member). If there is any IllegalAccessError, dynalink
adds the read link and tries to

unreflect again. We don't want unnecessary module link read in such
cases. Check has been added whether the package is exported from
declaring module. Note that there is no security issue here.  Even
before the fix, module read edge does not give any capability. unreflect
call after adding unnecessary read line would still fail for
non-exported package case. There were unnecessary module read links
created - which is being avoided now.

* Additional "API" in Lookup.java slipped from jigsaw code into
jdk9-dev. Those unreflectCallerSensitive and
unreflectConstructorCallerSensitive were meant to be 'interim' somehow
slipped.  Now, only unreflect and unreflectConstructor in Lookup. Caller
sensitiveness is hidden in the implementation.  These methods were never
APIs when dynalink API was created.

Thanks,

-Sundar