RFR: 8303588: [JVMCI] make JVMCI source directories conform with standard layout

[Doug Simon]

On Fri, 3 Mar 2023 18:02:22 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> The layout of the sources in `jdk.internal.vm.ci` stems from their initial development outside the JDK where they adopted a layout influenced by Eclipse.
>> 
>> There's no good reason for maintaining this layout any more. Moving to a standard layout also means IDEs will be able to make sense of the JVMCI sources in `src.zip`.
>
> Good.
> Please, test it in mach5.

Thanks for the review @vnkozlov . Since @tkrodriguez approved an internal review for these changes, I'm going to integrate.

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PR: https://git.openjdk.org/jdk/pull/12860