Fix INT64 initializer data propagation (#28778)
## Description
Fixes the in-memory `INT64` initializer materialization path in
`Graph::SaveShapeValuesFromDataPropagation`.
The `INT64` branch now validates the tensor element count and resizes
the destination `TensorShapeVector` before copying, matching the
behavior of the other initializer materialization branches.
## Testing
- Added a regression model that exercises the in-memory-external `INT64`
initializer path during graph re-resolution.
- Built `onnxruntime_test_all` with AddressSanitizer enabled on Windows
Debug.
- Verified the regression fails on unfixed `origin/main` under ASan.
- Verified the same regression passes with this fix under ASan:
```text
[ PASSED ] 1 test.
```
Focused test:
```text
ShapeInferenceV2Test.PartialDataPropagationTest
```
Co-authored-by: Gopalakrishnan Nallasamy <gnallasamy@microsoft.com>
