Convert Initializers to OrtValues Phase 2 (#25320)
### Description
Make protobuf weights refer to OrtValues on load.
Create OrtValues for initializers that are loaded from ORT format for
uniformity.
Create OrtValues for ORT format initializers.
Adjust exporting Graph::ToGraphProto() so it does not export in memory
references in external data.
Make CoreML process external data including in memory references so it
can copy it.
### Motivation and Context
Follow up for https://github.com/microsoft/onnxruntime/pull/23979
