Animation and Haptics: add ViewAnimatingPosition

Add the `ViewAnimationPosition` enumeration for implementing
`ViewImplicitlyAnimating`.

Author: compnerd

Sources/SwiftWin32/Animation and Haptics/Property-Based Animations/ViewAnimating.swift

@@ -0,0 +1,19 @@
+// Copyright © 2021 Saleem Abdulrasool <compnerd@compnerd.org>
+// SPDX-License-Identifier: BSD-3-Clause
+
+/// Constants indicating positions within the animation.
+public enum ViewAnimatingPosition: Int {
+  /// The end point of the animation. Use this constant when you want the final
+  /// values for any animatable properties — that is, you want to refer to the
+  /// values you specified in your animation blocks.
+  case end
+
+  /// The beginning of the animation. Use this constant when you want the
+  /// starting values for any animatable properties—that is, the values of the
+  /// properties before you applied any animations.
+  case start
+
+  /// The current position. Use this constant when you want the most recent
+  /// value set by an animator object.
+  case current
+}