RFR: 8346781: [JVMCI] Limit ServiceLoader to class initializers

[Doug Simon]

In the context of libgraal, the current use of ServiceLoader in JVMCI is problematic as libgraal does all class loading at image build time. There are static fields such as `JVMCIServiceLocator.cachedLocators` that need to be initialized [via reflection](https://github.com/oracle/graal/blob/30492c3f7847a13ae7f8dc50663a5a039e49a8e7/compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/libgraal/BuildTime.java#L175-L180) when building libgraal.

This PR removes the need for such reflection by moving all use of ServiceLoader in JVMCI into `<clinit>` methods. These methods are executed when building libgraal.

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Commit messages:
 - remove non-native-image build time use of ServiceLoader
 - make Cleaner.clean public

Changes: https://git.openjdk.org/jdk/pull/22869/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22869&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346781
  Stats: 166 lines in 7 files changed: 10 ins; 126 del; 30 mod
  Patch: https://git.openjdk.org/jdk/pull/22869.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22869/head:pull/22869

PR: https://git.openjdk.org/jdk/pull/22869