feat(slider): adds support for touch to seek to iOS slider (#117)

* feat(slider): adds support for touch to seek to iOS slider

* refactor(slider): adds tap to seek for ios

Author: shwetsolanki

src/ios/RNCSlider.m

@@ -10,6 +10,22 @@
 @implementation RNCSlider
 {
   float _unclippedValue;
+  UITapGestureRecognizer * tapGesturer;
+}
+
+- (instancetype)initWithFrame:(CGRect)frame
+{
+    self = [super initWithFrame:frame];
+    if (self) {
+        tapGesturer = [[UITapGestureRecognizer alloc] initWithTarget: self action:@selector(tapHandler:)];
+        [tapGesturer setNumberOfTapsRequired: 1];
+        [self addGestureRecognizer:tapGesturer];
+    }
+    return self;
+}
+- (void)tapHandler:(UITapGestureRecognizer *)gesture {
+    CGPoint touchPoint = [gesture locationInView:self];
+    [self setValue:touchPoint.x / self.bounds.size.width animated: YES];
 }
 
 - (void)setValue:(float)value
@@ -99,4 +115,8 @@ - (void)setInverted:(BOOL)inverted
   }
 }
 
+- (BOOL)beginTrackingWithTouch:(UITouch *)touch withEvent:(UIEvent *)event {
+    return YES;
+}
+
 @end