[MIGraphX EP] Set External Data Path (#21598)
### Description
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Changes to add in Set external data path for model weight files.
Additional fixes to ensure this compiles off the latest v1.19
Onnxruntime
### Motivation and Context
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- If it fixes an open issue, please link to the issue here. -->
Separate weights used for larger models (like stable diffusion) is
motivation for this change set
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Co-authored-by: Jeff Daily <jeff.daily@amd.com>
Co-authored-by: Artur Wojcik <artur.wojcik@amd.com>
Co-authored-by: Ted Themistokleous <tedthemistokleous@amd.com>
