Fix Android momentum scroll differences to iOS

- Momentum scroll events should not be emitted when there's no momentum
- Momentum scroll should be interrupted by a drag, which should not emit
  an onMomentumScrollEnd event. Instead a new momentum scroll should
  begin once dragging ends.

ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactHorizontalScrollView.java

@@ -246,6 +246,12 @@ public boolean onInterceptTouchEvent(MotionEvent ev) {
         ReactScrollViewHelper.emitScrollBeginDragEvent(this);
         mDragging = true;
         enableFpsListener();
+        // The user might be interrupting a fling/snap and we need to cancel any ongoing animations.
+        // Mirrors behaviour on iOS by starting a new momentum scroll event series after this drag.
+        if (mPostTouchRunnable != null) {
+          removeCallbacks(mPostTouchRunnable);
+          mPostTouchRunnable = null;
+        }
         return true;
       }
     } catch (IllegalArgumentException e) {
@@ -445,6 +451,12 @@ private void handlePostTouchScrolling(int velocityX, int velocityY) {
       return;
     }
 
+    // Don't emit momentum events if there's not going to be a momentum scroll, mirrors iOS momentum
+    // scroll behaviour.
+    if (!mPagingEnabled && velocityX == 0 && velocityY == 0) {
+      return;
+    }
+
     // Check if we are already handling this which may occur if this is called by both the touch up
     // and a fling call
     if (mPostTouchRunnable != null) {

ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollView.java

@@ -235,6 +235,12 @@ public boolean onInterceptTouchEvent(MotionEvent ev) {
         ReactScrollViewHelper.emitScrollBeginDragEvent(this);
         mDragging = true;
         enableFpsListener();
+        // The user might be interrupting a fling/snap and we need to cancel any ongoing animations.
+        // Mirrors behaviour on iOS by starting a new momentum scroll event series after this drag.
+        if (mPostTouchRunnable != null) {
+          removeCallbacks(mPostTouchRunnable);
+          mPostTouchRunnable = null;
+        }
         return true;
       }
     } catch (IllegalArgumentException e) {
@@ -412,6 +418,12 @@ private void handlePostTouchScrolling(int velocityX, int velocityY) {
       return;
     }
 
+    // Don't emit momentum events if there's not going to be a momentum scroll, mirrors iOS momentum
+    // scroll behaviour.
+    if (!mPagingEnabled && velocityX == 0 && velocityY == 0) {
+      return;
+    }
+
     // Check if we are already handling this which may occur if this is called by both the touch up
     // and a fling call
     if (mPostTouchRunnable != null) {