[code-reflection] RFR: Onnx model and protobuf model improvements [v4]

[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:

  Update ProtoGen.java

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Changes:
  - all: https://git.openjdk.org/babylon/pull/414/files
  - new: https://git.openjdk.org/babylon/pull/414/files/3fc910ee..ad654250

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=babylon&pr=414&range=03
 - incr: https://webrevs.openjdk.org/?repo=babylon&pr=414&range=02-03

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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