RFR: JDK-8210009: Source Launcher classloader should support getResource and getResourceAsStream

[Jonathan Gibbons]

Please review a change to add support for the getResource* group of methods
to the internal class loader used by the Source Launcher, introduced in 
JEP 330.

The overall issue has been discussed on OpenJDK lists, [1,2]

The implementation consists of providing findResource and findResources,
along with a couple of minor additional classes to implement 
URLStreamHandler
and URLConnection.

There is one implementation detail worthy of note. The "new URL" should
be inside a doPrivileged block, but overall, the Source Launcher does not
work when a security manager in installed. This is being tracked as 
JDK-8210274,
and the appropriate doPrivileged call will be added as part of that fix.

-- Jon

JBS: https://bugs.openjdk.java.net/browse/JDK-8210009
Webrev: http://cr.openjdk.java.net/~jjg/8210009/webrev.01/

[1] 
http://mail.openjdk.java.net/pipermail/compiler-dev/2018-August/012294.html
[2] 
http://mail.openjdk.java.net/pipermail/core-libs-dev/2018-August/055001.html