RFR: 8323832: Load JVMCI with the platform class loader [v2]

[Magnus Ihse Bursie]

On Tue, 23 Jan 2024 19:16:49 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

>> 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`.
>
> Doug Simon has updated the pull request incrementally with one additional commit since the last revision:
> 
>   use null to denote boot class loader as delegation parent

Build changes are trivially fine

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Marked as reviewed by ihse (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/17520#pullrequestreview-1841751451