[code-reflection] RFR: OnnxProtoModel implementation [v4]

[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 minor fixes

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

Changes:
  - all: https://git.openjdk.org/babylon/pull/399/files
  - new: https://git.openjdk.org/babylon/pull/399/files/c93d78ef..8271e2c3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=babylon&pr=399&range=03
 - incr: https://webrevs.openjdk.org/?repo=babylon&pr=399&range=02-03

  Stats: 72 lines in 1 file changed: 0 ins; 0 del; 72 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