add toDataURL method for svg elements

Add toDataURL method for svg elements to get data64 data  of svg.(iOS)
Add example for this.

ios/Elements/RNSVGSvgView.h

@@ -20,15 +20,11 @@
  * define <ClipPath></ClipPath> content as clipPath template.
  */
 - (void)defineClipPath:(__kindof RNSVGNode *)clipPath clipPathRef:(NSString *)clipPathRef;
-
 - (RNSVGNode *)getDefinedClipPath:(NSString *)clipPathRef;
-
 - (void)defineTemplate:(__kindof RNSVGNode *)template templateRef:(NSString *)templateRef;
-
 - (RNSVGNode *)getDefinedTemplate:(NSString *)tempalteRef;
-
 - (void)defineBrushConverter:(RNSVGBrushConverter *)brushConverter brushConverterRef:(NSString *)brushConverterRef;
-
 - (RNSVGBrushConverter *)getDefinedBrushConverter:(NSString *)brushConverterRef;
+- (NSString *)getDataURL;
 
 @end

ios/Elements/RNSVGSvgView.m

@@ -16,6 +16,7 @@
     NSMutableDictionary<NSString *, RNSVGNode *> *clipPaths;
     NSMutableDictionary<NSString *, RNSVGNode *> *templates;
     NSMutableDictionary<NSString *, RNSVGBrushConverter *> *brushConverters;
+    CGRect _boundingBox;
 }
 
 - (void)insertReactSubview:(UIView *)subview atIndex:(NSInteger)atIndex
@@ -47,6 +48,7 @@
     templates = nil;
     brushConverters = nil;
     CGContextRef context = UIGraphicsGetCurrentContext();
+    _boundingBox = rect;
     
     for (RNSVGNode *node in self.subviews) {
         if ([node isKindOfClass:[RNSVGNode class]]) {
@@ -63,10 +65,17 @@
             [node renderTo:context];
         }
     }
-//    CGImageRef image = CGBitmapContextCreateImage(context);
-//    NSData *imageData = UIImagePNGRepresentation([[UIImage alloc] initWithCGImage:image]);
-//    NSString *base64 = [imageData base64EncodedStringWithOptions:NSDataBase64Encoding64CharacterLineLength];
-//    NSLog(base64);
+}
+
+- (NSString *)getDataURL
+{
+    UIGraphicsBeginImageContextWithOptions(_boundingBox.size, NO, 0);
+    [self drawRect:_boundingBox];
+    UIImage * image = UIGraphicsGetImageFromCurrentImageContext();
+    NSData *imageData = UIImagePNGRepresentation(image);
+    NSString *base64 = [imageData base64EncodedStringWithOptions:NSDataBase64Encoding64CharacterLineLength];
+    UIGraphicsEndImageContext();
+    return base64;
 }
 
 - (void)reactSetInheritedBackgroundColor:(UIColor *)inheritedBackgroundColor