RFR: 8222144: Lazily create JRT code source URLs for LoadedModules

[Claes Redestad]

Hi,

currently we eagerly convert code source URIs to URLs to avoid recursive
bootstrap issues with overrideable URL handlers. The JRT scheme handler
is not overrideable, however, and also commonly used for all system
modules. Creating these URLs lazily is a reasonable startup
optimization since most applications will only ever load from a small
fraction of the resolved system modules.

Bug:    https://bugs.openjdk.java.net/browse/JDK-8222144
Webrev: http://cr.openjdk.java.net/~redestad/8222144/open.00/

Testing: tier1-2, improvements on all metrics on small startup tests

Thanks!

/Claes