RFR JDK-8038310: Re-examine integration of extended Charsets

[Xueming Shen]

Hi,

Please help review the change of changing the hard-wired extended charsets loading mechanism
to ServiceLoader.loadInstalled(), for the module system. With the fix for JDK-8069588 in JDK 9 all
charsets needed to startup in supported environments are in the base module. This change is to
use ServiceLoader to load the extended charsets to remove the java.base dependency on jdk.charsets
moduel.

Issues:
JDK-8038310: Re-examine integration of extended Charsets
JDK-8069588: Need to avoid attempting to load extended charsets (from jdk.charsets module) before module system initialization runs

webrev:
http://cr.openjdk.java.net/~sherman/8069588_8038310/webrev

Thanks
-Sherman