Fix plugin EP allocator deleter lifetime

[tianleiwu]

Cherrypick #29663 so that it can pass CI for 1.28 release.

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Summary

This PR fixes an AppVerifier failure seen during ONNX Runtime / onnxruntime_genai shutdown with the plugin EP path:

INVALID_POINTER_READ_AVRF_c0000005_onnxruntime.dll!OrtGetApiBase
Access violation - code c0000005

The bug is in the allocator deleter lifetime. Plugin EP allocators are released later by an OrtAllocatorUniquePtr custom deleter, but the deleter was reaching OrtEpFactory::ReleaseAllocator through transient owner captures:

• Environment::CreateSharedAllocatorImpl captured ep_device by reference.
• PluginExecutionProvider::CreatePreferredAllocators captured this.

The fix captures the required OrtEpFactory* directly in both deleters and calls:

ep_factory->ReleaseAllocator(ep_factory, allocator);

This keeps allocator destruction independent from the stack reference / provider object used when the deleter was created, while preserving the same allocator ownership and release API.

Changed files

• onnxruntime/core/session/environment.cc
• onnxruntime/core/session/plugin_ep/ep_plugin_provider_interfaces.cc

Verification

Built ORT and the TRT-RTX EP repro stack against TRT-RTX 1.6.1.114, then ran the DeepSeek WinML AppVerifier repro.

• Fixed branch: "appVerifierEnabled": true, "appVerifierFailed": false
• Rebuilt origin/main negative control: "appVerifierEnabled": true, "appVerifierFailed": true

This confirms the invalid pointer read still reproduces on origin/main and is removed by the allocator deleter lifetime change.