[code-reflection] RFR: Removal of OnnxType.Initializer type

[Paul Sandoz]

On Wed, 16 Apr 2025 09:43:37 GMT, Adam Sotona <asotona at openjdk.org> wrote:

> This PR removes `OnnxType.Initializer` type and it passes sequence of `FieldRef` of the initializers directly from `OnnxTransformer` to `OnnxRuntime` instead.

Marked as reviewed by psandoz (Lead).

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PR Review: https://git.openjdk.org/babylon/pull/396#pullrequestreview-2772994522