[code-reflection] RFR: OnnxProtoModel implementation [v2]

[Adam Sotona]

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

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

  OnnxProtoModel::toText improved to allow dump all data

-------------

Changes:
  - all: https://git.openjdk.org/babylon/pull/399/files
  - new: https://git.openjdk.org/babylon/pull/399/files/9748e144..a1930237

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=babylon&pr=399&range=01
 - incr: https://webrevs.openjdk.org/?repo=babylon&pr=399&range=00-01

  Stats: 16 lines in 1 file changed: 6 ins; 0 del; 10 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