Improve snapshot clearing consistency

Updated snapshot result to clear the
internal SkImage whenever the layer changes.
The previous logic did not clear out the snapshot
in various use cases. Because the implementation
before relied on the snapshot created with SkSurface
this makes the cleanup logic consistent with SkImages
created with SkImage::makeWithFilter

Bug: 188450217
Test: manual testing of discord app
Change-Id: I6391eb3b49794e54705bf5c6a09d2bdfd0564d05

libs/hwui/RenderNode.cpp

@@ -455,8 +455,7 @@ void RenderNode::destroyLayers() {
     if (hasLayer()) {
         this->setLayerSurface(nullptr);
     }
-    mSnapshotResult.snapshot = nullptr;
-    mTargetImageFilter = nullptr;
+
     if (mDisplayList) {
         mDisplayList.updateChildren([](RenderNode* child) { child->destroyLayers(); });
     }

libs/hwui/RenderNode.h

@@ -330,6 +330,11 @@ public:
         } else {
             mSkiaLayer.reset();
         }
+
+        // Clear out the previous snapshot and the image filter the previous
+        // snapshot was created with whenever the layer changes.
+        mSnapshotResult.snapshot = nullptr;
+        mTargetImageFilter = nullptr;
     }
 
     /**