Fix NodeAttrHelper string default lifetime

[Akshay Sonawane (apsonawane)]

This pull request enhances the NodeAttrHelper utility by adding overloads for retrieving string attributes with different types of default values, improving safety and flexibility when handling attribute lookups. It also updates usages to leverage these new overloads and clarifies ownership semantics for returned strings.

Node attribute retrieval improvements:

• Added two new overloads to NodeAttrHelper::Get for string attributes: one that accepts an rvalue (std::string&&) and one that accepts a C-style string (const char*). These overloads return owned strings, ensuring safe return of temporaries or literals. The documentation was updated to clarify that lvalue defaults may be returned by reference, while temporaries and literals are returned as owned strings. (onnxruntime/core/providers/qnn/ort_api.h [1] onnxruntime/core/providers/shared/utils/utils.h [2]
• Implemented the new overloads in both QNN and shared utility implementations of NodeAttrHelper. (onnxruntime/core/providers/qnn/ort_api.cc [1] onnxruntime/core/providers/shared/utils/utils.cc [2]
• Included <utility> header for std::move usage. (onnxruntime/core/providers/shared/utils/utils.cc onnxruntime/core/providers/shared/utils/utils.ccR7-R8)

Usage updates and bug fixes:

• Updated code to use the new overloads, such as switching from a reference to a temporary std::string for the default value in context binary retrieval, preventing potential dangling reference issues. (onnxruntime/core/providers/qnn/builder/onnx_ctx_model_helper.cc onnxruntime/core/providers/qnn/builder/onnx_ctx_model_helper.ccL94-R95)
• Fixed a usage in the VSINPU provider to use an owned string when retrieving the coordinate_transoformation_mode attribute, aligning with the new overloads and preventing reference issues. (onnxruntime/core/providers/vsinpu/builders/impl/resize_op_builder.h onnxruntime/core/providers/vsinpu/builders/impl/resize_op_builder.hL72-R72)