RFR(S) 8240205: Avoid PackageEntry lookup when loading shared classes

[Calvin Cheung]

RFE: https://bugs.openjdk.java.net/browse/JDK-8240205
webrev: http://cr.openjdk.java.net/~ccheung/jdk15/8240205/webrev.00/

During loading of a shared class from a CDS archive, the PackageEntry is 
being looked up in several places within the same call stack. This RFE 
is to do the PackageEntry lookup at one place and then pass it along to 
the subsequently called functions which need it.

Perf improvement on loading approx. 2000 classes on linux:

instr delta = -17930620 -0.6155%
time delta = -6.311 ms -0.7516%

Passed tiers1 - 4 testing.

thanks,

Calvin