Add EpoxySwiftUIHostingView (#619)

UI/UIx/SwiftUI/Epoxy/DataIDProviding.swift

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+// From: https://github.com/airbnb/epoxy-ios/blob/ecee1ace58d58e3cc918a2dea28095de713b1112
+
+// Created by eric_horacek on 12/1/20.
+// Copyright © 2020 Airbnb Inc. All rights reserved.
+
+// MARK: - DefaultDataID
+
+/// The default data ID when none is provided.
+public enum DefaultDataID: Hashable, CustomDebugStringConvertible {
+    case noneProvided
+
+    // MARK: Public
+
+    public var debugDescription: String {
+        "DefaultDataID.noneProvided"
+    }
+}

UI/UIx/SwiftUI/Epoxy/EpoxyIntrinsicContentSizeInvalidator.swift

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+// From: https://github.com/airbnb/epoxy-ios/blob/ecee1ace58d58e3cc918a2dea28095de713b1112
+
+// Created by matthew_cheok on 11/19/21.
+// Copyright © 2021 Airbnb Inc. All rights reserved.
+
+import SwiftUI
+
+// MARK: - EpoxyIntrinsicContentSizeInvalidator
+
+/// Allows the SwiftUI view contained in an Epoxy model to request the invalidation of
+/// the container's intrinsic content size.
+///
+/// ```
+/// @Environment(\.epoxyIntrinsicContentSizeInvalidator) var invalidateIntrinsicContentSize
+///
+/// var body: some View {
+///   ...
+///   .onChange(of: size) {
+///     invalidateIntrinsicContentSize()
+///   }
+/// }
+/// ```
+public struct EpoxyIntrinsicContentSizeInvalidator {
+    // MARK: Public
+
+    public func callAsFunction() {
+        invalidate()
+    }
+
+    // MARK: Internal
+
+    let invalidate: () -> Void
+}
+
+// MARK: - EnvironmentValues
+
+extension EnvironmentValues {
+    /// A means of invalidating the intrinsic content size of the parent `EpoxySwiftUIHostingView`.
+    public var epoxyIntrinsicContentSizeInvalidator: EpoxyIntrinsicContentSizeInvalidator {
+        get { self[EpoxyIntrinsicContentSizeInvalidatorKey.self] }
+        set { self[EpoxyIntrinsicContentSizeInvalidatorKey.self] = newValue }
+    }
+}
+
+// MARK: - EpoxyIntrinsicContentSizeInvalidatorKey
+
+private struct EpoxyIntrinsicContentSizeInvalidatorKey: EnvironmentKey {
+    static let defaultValue = EpoxyIntrinsicContentSizeInvalidator(invalidate: { })
+}

UI/UIx/SwiftUI/Epoxy/EpoxySwiftUIHostingController.swift

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+// From: https://github.com/airbnb/epoxy-ios/blob/ecee1ace58d58e3cc918a2dea28095de713b1112
+
+// Created by eric_horacek on 10/8/21.
+// Copyright © 2021 Airbnb Inc. All rights reserved.
+
+import SwiftUI
+
+#if !os(macOS)
+
+    // MARK: - EpoxySwiftUIUIHostingController
+
+    /// A `UIHostingController` that hosts SwiftUI views within an Epoxy container, e.g. an Epoxy
+    /// `CollectionView`.
+    ///
+    /// Exposed publicly to allow consumers to reason about these view controllers, e.g. to opt
+    /// collection view cells out of automated view controller impression tracking.
+    ///
+    /// - SeeAlso: `EpoxySwiftUIHostingView`
+    open class EpoxySwiftUIHostingController<Content: View>: UIHostingController<Content> {
+        // MARK: Lifecycle
+
+        /// Creates a `UIHostingController` that optionally ignores the `safeAreaInsets` when laying out
+        /// its contained `RootView`.
+        public convenience init(rootView: Content, ignoreSafeArea: Bool) {
+            self.init(rootView: rootView)
+
+            clearBackground()
+
+            // We unfortunately need to call a private API to disable the safe area. We can also accomplish
+            // this by dynamically subclassing this view controller's view at runtime and overriding its
+            // `safeAreaInsets` property and returning `.zero`. An implementation of that logic is
+            // available in this file in the `2d28b3181cca50b89618b54836f7a9b6e36ea78e` commit if this API
+            // no longer functions in future SwiftUI versions.
+            _disableSafeArea = ignoreSafeArea
+        }
+
+        // MARK: Open
+
+        override open func viewDidLoad() {
+            super.viewDidLoad()
+
+            clearBackground()
+        }
+
+        // MARK: Internal
+
+        func clearBackground() {
+            // A `UIHostingController` has a system background color by default as it's typically used in
+            // full-screen use cases. Since we're using this view controller to place SwiftUI views within
+            // other view controllers we default the background color to clear so we can see the views
+            // below, e.g. to draw highlight states in a `CollectionView`.
+            view.backgroundColor = .clear
+        }
+    }
+#endif