[code-reflection] RFR: Initializers through arguments

[Adam Sotona]

Initializers through arguments implementation.
This PR is chained to ongoing work on `If` and `Loop` due to conflicting changes in `OnnxProtoBuilder`.

Input image reshape has to be removed from the CNN model due to unexpected exceptions in `Conv` op in relation with initializers.

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Commit messages:
 - MNISTDemo using initializers
 - removed obsolete test
 - re-enable tests
 - Removed Reshape from CNNTest to avoid model Conv exception when used with initialized weights
 - initializers through arguments - work in progress
 - initializers as parameters prefix
 - removed debug print
 - improved SimpleTest
 - Fixed captured tensors in If op model
 - sealed ExplicitOnnxOps
 - ... and 16 more: https://git.openjdk.org/babylon/compare/72a9d699...5843369d

Changes: https://git.openjdk.org/babylon/pull/340/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=340&range=00
  Stats: 767 lines in 12 files changed: 534 ins; 181 del; 52 mod
  Patch: https://git.openjdk.org/babylon/pull/340.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/340/head:pull/340

PR: https://git.openjdk.org/babylon/pull/340