[Plugin WebGPU EP] Fix API initialization error handling (#28211)
### Description
<!-- Describe your changes. -->
This pull request improves error handling in the `CreateEpFactories`
function in `onnxruntime/core/providers/webgpu/ep/api.cc`.
The main enhancement is the addition of a more conservative mechanism
for creating `OrtStatus` objects when exceptions occur during API
initialization.
The existing code was attempting to create a C++ API `Ort::Status`
instance even if the API was not initialized successfully.
### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
Fix crash that was hiding underlying error message.