fix issue that render texture will have wrong effect if using with global z order (#18629)

Author: minggo

cocos/2d/CCRenderTexture.cpp

@@ -771,6 +771,12 @@ void RenderTexture::draw(Renderer *renderer, const Mat4 &transform, uint32_t fla
     }
 }
 
+void RenderTexture::setGlobalZOrder(float globalZOrder)
+{
+    Node::setGlobalZOrder(globalZOrder);
+    _sprite->setGlobalZOrder(globalZOrder);
+}
+
 void RenderTexture::begin()
 {
     Director* director = Director::getInstance();
@@ -805,15 +811,17 @@ void RenderTexture::begin()
     renderer->addCommand(&_groupCommand);
     renderer->pushGroup(_groupCommand.getRenderQueueID());
 
-    _beginCommand.init(_globalZOrder);
+    // Begine command should be the first command of the command group.
+    _beginCommand.init(INT_MIN);
     _beginCommand.func = CC_CALLBACK_0(RenderTexture::onBegin, this);
 
     Director::getInstance()->getRenderer()->addCommand(&_beginCommand);
 }
 
 void RenderTexture::end()
 {
-    _endCommand.init(_globalZOrder);
+    // End command should be the last command of the command group.
+    _endCommand.init(INT_MAX);
     _endCommand.func = CC_CALLBACK_0(RenderTexture::onEnd, this);
 
     Director* director = Director::getInstance();

cocos/2d/CCRenderTexture.h

@@ -264,6 +264,7 @@ class CC_DLL RenderTexture : public Node
     // Overrides
     virtual void visit(Renderer *renderer, const Mat4 &parentTransform, uint32_t parentFlags) override;
     virtual void draw(Renderer *renderer, const Mat4 &transform, uint32_t flags) override;
+    virtual void setGlobalZOrder(float globalZOrder) override;
 
     /** Flag: Use stack matrix computed from scene hierarchy or generate new modelView and projection matrix.
      *