[code-reflection] RFR: Support storing the code that builds the code model [v19]

[Paul Sandoz]

On Wed, 19 Mar 2025 03:20:56 GMT, Mourad Abbay <mabbay at openjdk.org> wrote:

>> In this PR we allow the user to decide how to store the code model. The first option is `TEXT`, if this is selected, we store the textual representation of the code model. The second option is `CODE_BUILDR`, if this is selected, we store the code that builds the code model. All work done here is around the second option, because the first option is already supported.
>
> Mourad Abbay has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Don't rely on the assumption of 1d array

I cannot tell what may be left to address for Maurizio's comments and what we can defer. If Maurizio is ok to integrate then i am ok.

It seems we can follow up later on the following:
- avoiding the insertion of Vars
- uniformity of method signatures that produce code models
- adjust the new operation to support an invocation descriptor attribute, similar to the invoke operation.

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PR Review: https://git.openjdk.org/babylon/pull/305#pullrequestreview-2714997295