⭐️ Impl: Add RNIModalError

Related:
* `TODO:2023-03-27-23-55-09` Refactor: Re-write `RNIModalView` error creation and handling.

ios/src_library/React Native/RNIModal/RNIModalError.swift

@@ -0,0 +1,41 @@
+//
+//  RNIModalError.swift
+//  react-native-ios-modal
+//
+//  Created by Dominic Go on 5/10/23.
+//
+
+import Foundation
+
+public enum RNIModalErrorCode: String, RNIErrorCode {
+  case modalAlreadyVisible,
+       modalAlreadyHidden,
+       dismissRejected;
+};
+
+public struct RNIModalError: RNIError {
+
+  public typealias ErrorCode = RNIModalErrorCode;
+
+  public static var domain = "react-native-ios-modal";
+
+  public var code: RNIModalErrorCode;
+  public var message: String?;
+
+  public var debugMessage: String?;
+  public var debugData: Dictionary<String, Any>?;
+
+  public var fileID: String?;
+  public var functionName: String?;
+  public var lineNumber: Int?;
+
+  public init(
+    code: ErrorCode,
+    message: String?,
+    debugMessage: String?
+  ) {
+    self.code = code;
+    self.message = message;
+    self.debugMessage = debugMessage;
+  };
+};