RFR: 8323832: Load JVMCI with the platform class loader

[Doug Simon]

This PR changes `jdk.internal.vm.ci` such that it is loaded by the platform class loader instead of the boot class loader. This allows Native Image to load a version of JVMCI different than the version on top of which Native Image is running. This capability is demonstrated and tested by `LoadAlternativeJVMCI.java`.

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Commit messages:
 - load JVMCI with platform class loader

Changes: https://git.openjdk.org/jdk/pull/17520/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17520&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323832
  Stats: 227 lines in 8 files changed: 219 ins; 1 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/17520.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17520/head:pull/17520

PR: https://git.openjdk.org/jdk/pull/17520