[code-reflection] RFR: OnnxProtoModel implementation

[Adam Sotona]

Changes in this PR:
- `OnnxProtoModel` implementation replacing and enhancing basic `OnnxProtoPrinter` functionality
- added missing copyright headers

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Commit messages:
 - copyright headers
 - fixed OnnxProtoModel
 - Merge remote-tracking branch 'babylon/code-reflection' into onnx-parser
 - OnnxProtoModel implementation replaces OnnxProtoPrinter
 - draft of ModelProto
 - draft of OnnxProtoParser
 - draft of OnnxProtoParser
 - draft of OnnxProtoParser
 - OnnxProtoPrinter improvements

Changes: https://git.openjdk.org/babylon/pull/399/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=399&range=00
  Stats: 787 lines in 7 files changed: 531 ins; 256 del; 0 mod
  Patch: https://git.openjdk.org/babylon/pull/399.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/399/head:pull/399

PR: https://git.openjdk.org/babylon/pull/399