RFR: 8282986: Inconsistent naming of "system" class loader

[Ioi Lam]

On Fri, 1 Jul 2022 19:02:12 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> This is a somewhat trivial renaming.  Ran the CDS tests locally.

I also updated the [bug report](https://bugs.openjdk.org/browse/JDK-8282986)'s Description to say that we are leaving `SystemDictionary::_java_system_loader` as is.

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PR: https://git.openjdk.org/jdk/pull/9349