[code-reflection] RFR: Onnx model and protobuf model improvements [v2]

[Adam Sotona]

> Onnx model and protobuf model improvements.
> Onnx protobuf constants, builder and model generated.

Adam Sotona has updated the pull request incrementally with one additional commit since the last revision:

  NIT ProtoGen fix

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Changes:
  - all: https://git.openjdk.org/babylon/pull/414/files
  - new: https://git.openjdk.org/babylon/pull/414/files/3be8f709..6d2adfa1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=babylon&pr=414&range=01
 - incr: https://webrevs.openjdk.org/?repo=babylon&pr=414&range=00-01

  Stats: 3 lines in 2 files changed: 1 ins; 2 del; 0 mod
  Patch: https://git.openjdk.org/babylon/pull/414.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/414/head:pull/414

PR: https://git.openjdk.org/babylon/pull/414