Add support for animating z position. (#96)

Author: jverkoey

src/MDMAnimatableKeyPaths.h

@@ -218,3 +218,13 @@ FOUNDATION_EXPORT MDMAnimatableKeyPath MDMKeyPathX NS_SWIFT_NAME(x);
  Additive animation supported: Yes.
  */
 FOUNDATION_EXPORT MDMAnimatableKeyPath MDMKeyPathY NS_SWIFT_NAME(y);
+
+/**
+ Z position.
+
+ Equivalent UIView property: N/A
+ Equivalent CALayer property: zPosition
+ Expected value type: CGFloat or NSNumber.
+ Additive animation supported: Yes.
+ */
+FOUNDATION_EXPORT MDMAnimatableKeyPath MDMKeyPathZ NS_SWIFT_NAME(z);

src/MDMAnimatableKeyPaths.m

@@ -33,3 +33,4 @@
 MDMAnimatableKeyPath MDMKeyPathWidth = @"bounds.size.width";
 MDMAnimatableKeyPath MDMKeyPathX = @"position.x";
 MDMAnimatableKeyPath MDMKeyPathY = @"position.y";
+MDMAnimatableKeyPath MDMKeyPathZ = @"zPosition";

src/private/MDMBlockAnimations.m

@@ -43,7 +43,8 @@
                                                MDMKeyPathTransform,
                                                MDMKeyPathWidth,
                                                MDMKeyPathX,
-                                               MDMKeyPathY]];
+                                               MDMKeyPathY,
+                                               MDMKeyPathZ]];
   });
   return animatableKeyPaths;
 }

tests/unit/MotionAnimatorBehavioralTests.swift

@@ -60,6 +60,7 @@ class AnimatorBehavioralTests: XCTestCase {
     .width: 25,
     .x: 12,
     .y: 23,
+    .z: 3,
   ]
 
   func testAllKeyPathsExplicitlyAnimateWithLayerBackingUIView() {

tests/unit/QuartzCoreBehavioralTests.swift

@@ -85,6 +85,7 @@ class QuartzCoreBehavioralTests: XCTestCase {
       .width: 25,
       .x: 12,
       .y: 23,
+      .z: 3,
     ]
     for (keyPath, value) in properties {
       rebuildLayer()

tests/unit/UIKitBehavioralTests.swift

@@ -144,6 +144,7 @@ class UIKitBehavioralTests: XCTestCase {
       .shadowRadius: 5,
       .strokeStart: 0.2,
       .strokeEnd: 0.5,
+      .z: 3,
     ]
 
     let properties: [AnimatableKeyPath: Any]

tests/unit/UIKitEquivalencyTests.swift

@@ -69,6 +69,7 @@ class UIKitEquivalencyTests: XCTestCase {
       .transform: CGAffineTransform(scaleX: 1.5, y: 1.5),
       .x: 12,
       .y: 23,
+      .z: 3,
 
       // Should animate additively, but blocked by
       // https://github.com/material-motion/motion-animator-objc/issues/74