[code-reflection] RFR: Remove ExternalizableOp

[Maurizio Cimadamore]

On Wed, 25 Jun 2025 19:13:43 GMT, Paul Sandoz <psandoz at openjdk.org> wrote:

> Remove `ExternalizableOp` and allow any `Op` to externalize its specific state. Remove `ExternalizableTypeElement` and allow any `TypeElement` to externalize its state.
> 
> Add a `Location` component to `ExternalizedOp`, instead of including in an externalized operations specific state (map of attributes).

Looks good, I agree the exposed API seems simpler.

Now that externalization is a more "official" part of ops and type elements, I wonder if having a separate `extern` package still makes sense.

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Marked as reviewed by mcimadamore (Reviewer).

PR Review: https://git.openjdk.org/babylon/pull/464#pullrequestreview-2961715056
PR Comment: https://git.openjdk.org/babylon/pull/464#issuecomment-3008123014