Canonicalize external data locations (#32135)
This pull request improves the robustness and correctness of handling
external data references in ONNX Runtime, particularly focusing on
rejecting invalid or ambiguous "location" entries and ensuring in-memory
reference tags are not treated as file paths. The changes also enhance
path validation logic and add new unit tests to cover these scenarios.
**Validation and error handling improvements:**
- Added a check in `ExternalDataInfo::Create` to reject duplicate
"location" entries in the external data info, ensuring only one
"location" is allowed per tensor.
[[1]](diffhunk://#diff-df6326d7af04c52e54c61249ff8b1980da9bac81192ee2e63c5b2280d7b91e05R32)
[[2]](diffhunk://#diff-df6326d7af04c52e54c61249ff8b1980da9bac81192ee2e63c5b2280d7b91e05L42-R47)
- Updated path validation logic in `ValidateExternalDataPathFromDir` and
`ValidateExternalDataPath` to explicitly reject in-memory reference tags
(used for internal memory mapping) as invalid file paths, alongside
empty and absolute paths.
[[1]](diffhunk://#diff-d31e9fbe0f5334fcd949833e035f2b25d5ae810dcd505c545f6b372b546b1406L410-R417)
[[2]](diffhunk://#diff-d31e9fbe0f5334fcd949833e035f2b25d5ae810dcd505c545f6b372b546b1406L423-R437)
[[3]](diffhunk://#diff-d31e9fbe0f5334fcd949833e035f2b25d5ae810dcd505c545f6b372b546b1406L438-R446)
[[4]](diffhunk://#diff-d31e9fbe0f5334fcd949833e035f2b25d5ae810dcd505c545f6b372b546b1406L448-R457)
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[[6]](diffhunk://#diff-d31e9fbe0f5334fcd949833e035f2b25d5ae810dcd505c545f6b372b546b1406L497-R509)
**Functionality and code clarity:**
- Refined `HasExternalDataInMemory` to correctly detect in-memory
references even if there are multiple "location" entries, improving
reliability.
**Testing enhancements:**
- Added new unit tests to verify that duplicate "location" entries are
rejected and that in-memory reference tags are correctly handled and
rejected by validation logic.
[[1]](diffhunk://#diff-d75ec5db9cc4642f78b6ff568aff6d10398fc211b0fb7c862d3ec88738e3eda6R146-R188)
[[2]](diffhunk://#diff-d75ec5db9cc4642f78b6ff568aff6d10398fc211b0fb7c862d3ec88738e3eda6R771-R782)
These changes collectively strengthen the validation of external data
references, prevent ambiguous or invalid configurations, and ensure that
in-memory tags are never misinterpreted as file paths.
