RFR: 8241371: Refactor and consolidate package_from_name

[Claes Redestad]

Hi,

JDK-8153858 partially consolidated the logic shared between
InstanceKlass::package_from_name and ClassLoader::package_from_name.
Unfortunately it also caused an undetected regression in some paths due
need to copy from Symbol -> resource arrays and back again.

By refactoring package_from_name into a single implementation which
operates on a Symbol* rather than a char* we can both simplify a bit
and regain some lost performance:

http://cr.openjdk.java.net/~redestad/scratch/pkg_lookups.00/

Testing: tier1-5, verified a ~0.5% improvement on startup

Thanks!

/Claes