RevenueCatUI: fix CocoaPods build (#3594)

Fixes https://circleci.com/gh/RevenueCat/purchases-ios/163464
Unfortunately CocoaPods does not support symlinks, and neither `pod spec
lint` nor our installation tests (because they use a local reference)
can catch that.
This replaces it with a copy of the file.

RevenueCatUI/Helpers/Optional+Extensions.swift

@@ -0,0 +1,46 @@
+//
+//  Copyright RevenueCat Inc. All Rights Reserved.
+//
+//  Licensed under the MIT License (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//      https://opensource.org/licenses/MIT
+//
+//  Optional+Extensions.swift
+//
+//  Created by Nacho Soto on 3/30/22.
+
+import Foundation
+
+/// Protocol definition to be able to use `Optional` as a type.
+internal protocol OptionalType {
+
+    associatedtype Wrapped
+
+    init(optional: Wrapped?)
+    var asOptional: Wrapped? { get }
+
+}
+
+extension Optional: OptionalType {
+
+    init(optional: Wrapped?) { self = optional }
+
+    var asOptional: Wrapped? { return self }
+
+}
+
+extension OptionalType {
+
+    /// - Returns: unwrapped value if present.
+    /// - Throws: `error` if the value is not present.
+    func orThrow(_ error: @autoclosure () -> Error) throws -> Wrapped {
+        if let value = self.asOptional {
+            return value
+        } else {
+            throw error()
+        }
+    }
+
+}