Native Animated - Add tests on iOS

Summary:
Adds unit tests to the Native Animated implementation on iOS. This pretty much mirrors the tests we currently have on Android.

It also fixes 2 bugs I've found when adding the tests and pass the current time in `stepAnimation` instead of using `CACurrentMediaTime` to make testing easier.

- `stopListeningToAnimatedNodeValue` did not actually work at all, it should set the listener to nil.
- The finished value in the animation end callback was always true, this simplifies the `RCTAnimationDriver` interface to get rid of `removeAnimation` and fixes the end callback value.

**Test plan**
- Run the tests
- Make sure the UIExplorer example still works
Closes https://github.com/facebook/react-native/pull/13068

Differential Revision: D4786701

Pulled By: javache

fbshipit-source-id: a4f07e6eec1f363ca47b6f27984041793c915bfc

Libraries/NativeAnimation/Nodes/RCTInterpolationAnimatedNode.m

@@ -8,6 +8,7 @@
  */
 
 #import "RCTInterpolationAnimatedNode.h"
+
 #import "RCTAnimationUtils.h"
 
 @implementation RCTInterpolationAnimatedNode
@@ -53,20 +54,6 @@
   }
 }
 
-- (NSUInteger)findIndexOfNearestValue:(CGFloat)value
-                              inRange:(NSArray<NSNumber *> *)range
-{
-  NSUInteger index;
-  NSUInteger rangeCount = range.count;
-  for (index = 1; index < rangeCount - 1; index++) {
-    NSNumber *inputValue = range[index];
-    if (inputValue.doubleValue >= value) {
-      break;
-    }
-  }
-  return index - 1;
-}
-
 - (void)performUpdate
 {
   [super performUpdate];
@@ -75,19 +62,12 @@
   }
 
   CGFloat inputValue = _parentNode.value;
-  NSUInteger rangeIndex = [self findIndexOfNearestValue:inputValue inRange:_inputRange];
-  NSNumber *inputMin = _inputRange[rangeIndex];
-  NSNumber *inputMax = _inputRange[rangeIndex + 1];
-  NSNumber *outputMin = _outputRange[rangeIndex];
-  NSNumber *outputMax = _outputRange[rangeIndex + 1];
 
-  self.value = RCTInterpolateValue(inputValue,
-                                   inputMin.doubleValue,
-                                   inputMax.doubleValue,
-                                   outputMin.doubleValue,
-                                   outputMax.doubleValue,
-                                   _extrapolateLeft,
-                                   _extrapolateRight);
+  self.value = RCTInterpolateValueInRange(inputValue,
+                                          _inputRange,
+                                          _outputRange,
+                                          _extrapolateLeft,
+                                          _extrapolateRight);
 }
 
 @end