Accept legacy WebGPU/WebNN memory info names for backward compatibility (#27637)
### Description
Accept pre-1.25 names `"WebGPU_Buffer"`/`"WebNN_Tensor"` as aliases in
`CreateMemoryInfo` and normalize them to the current short names
`"WebGPU_Buf"`/`"WebNN_Ten"`.
This is the **reverse** of
https://github.com/microsoft/onnxruntime/pull/27475 (which added forward
compatibility in the 1.24.x patch branch).
### Motivation and Context
Released onnxruntime-genai still uses the old (pre-1.25) long names when
calling `CreateMemoryInfo`. Without this change, those calls fail with
`ORT_INVALID_ARGUMENT` on main branch.
### Key Design Decision
When an old name is detected, it is **normalized** to the current short
constant (e.g., `"WebGPU_Buffer"` -> `"WebGPU_Buf"`). This is critical
because downstream code (e.g., `external_data_loader.cc`,
`webgpu_context.cc`) compares `OrtMemoryInfo.name` against the current
constants. Simply passing through the old name would cause those
comparisons to fail.
### Changes
- `onnxruntime/core/framework/allocator.cc`: Accept and normalize legacy
names in `CreateMemoryInfo`
- `onnxruntime/test/shared_lib/test_allocator.cc`: Add test verifying
legacy names are accepted and normalized
### See Also
- https://github.com/microsoft/onnxruntime/pull/27207 (original rename)
- https://github.com/microsoft/onnxruntime/pull/27475 (forward compat in
1.24.x)
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>