[code-reflection] RFR: OnnxProtoBuilder simplifications [v3]

[Adam Sotona]

> OnnxProtoBuilder simplifications

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

  OnnxInterpreter patch related to optional inputs

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

Changes:
  - all: https://git.openjdk.org/babylon/pull/324/files
  - new: https://git.openjdk.org/babylon/pull/324/files/6bb2c106..3eb31c5a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=babylon&pr=324&range=02
 - incr: https://webrevs.openjdk.org/?repo=babylon&pr=324&range=01-02

  Stats: 11 lines in 1 file changed: 2 ins; 8 del; 1 mod
  Patch: https://git.openjdk.org/babylon/pull/324.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/324/head:pull/324

PR: https://git.openjdk.org/babylon/pull/324