EP bridge: onnx-light called by ORT

onnx_light_ort::bridge_ep_light_called_by_ort is currently an interface target. It depends on Shared support for onnx-light in ORT, independently of Custom-op bridge: onnx-light called by ORT.

The future Custom execution provider library will use this bridge for EP-specific capability selection, kernel-registry and executable-partition adaptation. It shares native execution, buffer validation and status conversion through the common library rather than importing custom-op callbacks or its attribute contract. EP kernel factories must define their own standard-node defaults.

Runtime implementation and executable tests remain planned. The first implementation must add factory/kernel lifecycle, supported/unsupported node selection and real-ORT placement tests; an interface target alone is not evidence that an EP works.