Replace Objective-C bridge with Swift ONNX runtime backend

swift/OnnxRuntimeBindings/ORTError.swift

@@ -0,0 +1,21 @@
+import Foundation
+
+public enum ORTError: Error, LocalizedError {
+    case notImplemented(String)
+    case runtimeFailure(action: String, message: String)
+    case invalidArgument(String)
+    case unsupported(String)
+
+    public var errorDescription: String? {
+        switch self {
+        case .notImplemented(let symbol):
+            return "ONNX Runtime Swift interface symbol is not implemented yet: \(symbol)"
+        case .runtimeFailure(let action, let message):
+            return "\(action) failed: \(message)"
+        case .invalidArgument(let message):
+            return message
+        case .unsupported(let message):
+            return message
+        }
+    }
+}