RFR: 8350263: JvmciNotifyBootstrapFinishedEventTest intermittently times out

[Doug Simon]

[JDK-8346781](https://bugs.openjdk.org/browse/JDK-8346781) changed `JVMCIServiceLocator` such that set of providers is computed eagerly in `JVMCIServiceLocator.<clinit>`. There are some JVMCI test classes that directly subclassed `JVMCIServiceLocator` which meant deadlock could occur between the main thread running the test and a JVMCI compiler thread. This PR fixes this by ensuring that `JVMCIServiceLocator` providers are separate classes from the main test class.

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Commit messages:
 - avoid JVMCIServiceLocator related deadlock

Changes: https://git.openjdk.org/jdk/pull/23679/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23679&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8350263
  Stats: 60 lines in 4 files changed: 21 ins; 12 del; 27 mod
  Patch: https://git.openjdk.org/jdk/pull/23679.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23679/head:pull/23679

PR: https://git.openjdk.org/jdk/pull/23679