ExportModelForInferencing should use External Data if Necessary

[Whadup]

When storing large models, the export routine should decide to use external data.

Currently, external data is only used when the checkpoint is already using external data.

onnxruntime/orttraining/orttraining/training_api/module.cc

Line 688 in d27fecd

if (state_->has_external_data) {

However, exporting Model plus Checkpoint might make usage of external data necessary, as the result is larger than 2gb, while both model and checkpoint on their own might be smaller than 2gb.

[github-actions]

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