Split OnnxRuntime into high-level and low-level generated code

[mcimadamore]

This PR reorganizes the code in the OnnxRuntime class. It now contains an higher-level implementation of the onnx C API, which is separate from the low-level bindings. These bindings are defined in the new foreign package, and have been mechanically generated with a tweaked version of jextract which:

• omits some of the code that is not required (e.g. struct getters/setters)
• make the generated code more usable for onnx use case -- meaning each struct field should have an "invoker" accessor, which fetches the struct pointer and then invokes it

The generated code is still quite big (OrtApi struct contains 10K LoC). I can make the bindings smaller if we only want to focus on the handful of functions we use today -- but in its current form, the low-level bindings are "complete" and support the full C API.

The main changes in OnnxRuntime are as follows:

• calls to function pointers in OrtApi/OrtApiBase now are handled as calls to static wrappers generated by jextract.
• there's no need to try/catch and wrap exceptions because the generated code does that
• some of the explicit reinterpret calls with an explicit size have been replaced by generated reinterpret methods (which use the correct struct layout size)
• some of the constants (logging level, API version) are now taken from the generated code

When doing this exercise, I uncovered an issue with the MHs for a couple of functions (ReleaseEnv and ReleaseSession) being incorrect -- the underlying function pointers for these are void (so no result) and they don't accept a trailing ret segment. Also calling checkStatus on them makes no sense (again, because these functions don't return a status).

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[openjdk]

@mcimadamore This change now passes all automated pre-integration checks.

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Split OnnxRuntime into high-level and low-level generated code

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• 02: Full (343501dc)
• 01: Full - Incremental (fe746c01)
• 00: Full (5d8f9b03)

[openjdk]

@mcimadamore this pull request can not be integrated into code-reflection due to one or more merge conflicts. To resolve these merge conflicts and update this pull request you can run the following commands in the local repository for your personal fork:

git checkout onnx_jextract
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git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge code-reflection"
git push

[mcimadamore]

I've added some changes to make sure that the segments returned by the high-level API keep the automatic arena reachable. There are two places where I've added a reinterpret:

• retAddr -- as the output parameter ret is accessed, a segment is read (which will have no arena)
• run -- this also features output parameters (outputs) so we need to keep the segments read from these output parameters connected to the automatic arena

[openjdk]

@mcimadamore Please do not rebase or force-push to an active PR as it invalidates existing review comments. Note for future reference, the bots always squash all changes into a single commit automatically as part of the integration. See OpenJDK Developers’ Guide for more information.

[mcimadamore]

/integrate

[openjdk]

Going to push as commit 4752b37.

[openjdk]

@mcimadamore Pushed as commit 4752b37.

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