[Plugin EP] Port graph capture/replay APIs (#27958)
## Description
Ports graph capture/replay APIs (e.g., CUDA Graph) to the Plugin EP
(`OrtEp`) C API so that plugin-based execution providers can participate
in ORT-managed graph capture and replay.
### What changed
**New Plugin EP C API functions** (`onnxruntime_ep_c_api.h`):
- `OrtEp::IsGraphCaptureEnabled` — indicates whether the EP has graph
capture enabled.
- `OrtEp::IsGraphCaptured` — indicates whether a graph has been captured
for a given annotation ID.
- `OrtEp::ReplayGraph` — replays a previously captured graph.
- `OrtEp::GetGraphCaptureNodeAssignmentPolicy` — returns the node
assignment validation policy for graph capture.
All four are optional (NULL defaults to safe behavior) and version-gated
(`ort_version_supported >= 26`).
If `IsGraphCaptureEnabled` returns true, `IsGraphCaptured` and
`ReplayGraph` must also be implemented.
otherwise `PluginExecutionProvider` logs a warning and disables graph
capture for that EP.
**New `OrtGraphCaptureNodeAssignmentPolicy` enum**
(`onnxruntime_ep_c_api.h`):
Replaces the hardcoded EP-name checks in
`InferenceSession::Initialize()` with a policy-based approach:
- `ALL_NODES_ON_EP` — all nodes must be on the target EP (e.g.,
TensorRT).
- `ALLOW_CPU_FOR_SHAPES` — CPU nodes allowed for shape computation if no
memcpy nodes exist (e.g., CUDA, WebGPU, DML).
**Refactored `InferenceSession` graph capture selection**
(`inference_session.cc`):
- Removed the hardcoded `graph_support_ep_list` and per-EP `strcmp`
checks.
- Now iterates over all registered EPs and uses
`IsGraphCaptureEnabled()` + `GetGraphCaptureNodeAssignmentPolicy()` to
select and validate the graph-capturing EP.
- `AreAllComputeNodesAssignedToCudaOrJsOrDmlEpWebGpuEp()` → generalized
to `AreAllComputeNodesAssignedToEpOrCpu()`, which also requires at least
one node on the target EP.
- `IExecutionProvider::GetGraphCaptureNodeAssignmentPolicy()` added to
the base class (defaults to `ALL_NODES_ON_EP`).
**Bounded graph capture recursion** (`inference_session.cc/h`):
- `Run()` now delegates to `RunImpl()` with a `graph_capture_depth`
parameter.
- Caps internal run attempts at `kMaxGraphCaptureRunAttempts = 8`,
returning a clear error if the EP never reports `IsGraphCaptured() ==
true`.
**EP implementations**:
- **WebGPU plugin EP**: Fully implements all four graph capture APIs by
forwarding to the underlying `IExecutionProvider`.
- **CUDA plugin EP**: Stubs with TODOs (returns
disabled/not-implemented).
- **NvTensorRTRTX EP**: `IsGraphCaptureEnabled()` now returns `false`
since this EP manages graph capture internally (not via ORT).
**C++ wrapper** (`onnxruntime_cxx_api.h` / `onnxruntime_cxx_inline.h`):
- Added `Ort::Env::CopyTensor()` convenience overload for copying a
single tensor (wraps `CopyTensors` with `num_tensors=1`).
### Tests
- **`ep_plugin_provider_test.cc`**: Unit tests for each new
`PluginExecutionProvider` graph capture method, including NULL function
pointer defaults, version < 26 backward compatibilities, and validation
that `IsGraphCaptureEnabled()` returns false when `IsGraphCaptured` or
`ReplayGraph` are NULL.
- **`test_graph_capture.cc`**: End-to-end test for WebGPU plugin EP
graph capture/replay using IO binding (warm-up + capture run, then
replay with different inputs).
### Motivation and Context
Previously, graph capture support was limited to a hardcoded list of EPs
(`kCudaExecutionProvider`, `kTensorrtExecutionProvider`,
`kJsExecutionProvider`, `kWebGpuExecutionProvider`,
`kDmlExecutionProvider`) with EP-specific validation logic in
`InferenceSession`. This made it impossible for plugin EPs to
participate in ORT-managed graph capture/replay without modifying the
core session code.
This PR makes graph capture/replay extensible to any EP, including
out-of-tree plugin EPs, by exposing it through the `OrtEp` C API.
