Fix CGMutablePathRef memory leaks when the path is invalid. (flutter#14275)

Author: zhongwuzw

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.mm

@@ -4,6 +4,7 @@
 
 #include "flutter/shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h"
 
+#include "flutter/fml/platform/darwin/cf_utils.h"
 #include "flutter/shell/platform/darwin/ios/ios_surface.h"
 
 static int kMaxPointsInVerb = 4;
@@ -131,15 +132,14 @@ - (void)clipRRect:(const SkRRect&)clipSkRRect {
 }
 
 - (void)clipPath:(const SkPath&)path {
-  CGMutablePathRef pathRef = CGPathCreateMutable();
   if (!path.isValid()) {
     return;
   }
+  fml::CFRef<CGMutablePathRef> pathRef(CGPathCreateMutable());
   if (path.isEmpty()) {
     CAShapeLayer* clip = [[[CAShapeLayer alloc] init] autorelease];
     clip.path = pathRef;
     self.layer.mask = clip;
-    CGPathRelease(pathRef);
     return;
   }
 
@@ -197,7 +197,6 @@ - (void)clipPath:(const SkPath&)path {
   CAShapeLayer* clip = [[[CAShapeLayer alloc] init] autorelease];
   clip.path = pathRef;
   self.layer.mask = clip;
-  CGPathRelease(pathRef);
 }
 
 - (void)setClip:(flutter::MutatorType)type