widgets/cliprect: use layer.effect on content item over property

ShaderEffectSource as a property not parented to an item does not
update its sourceItem's QQuickWindow when its own is changed. This
lead to use after frees and broken effects when using ClippingRectangle.

src/widgets/ClippingRectangle.qml

@@ -1,3 +1,5 @@
+pragma ComponentBehavior: Bound
+
 import QtQuick
 
 ///! Rectangle capable of clipping content inside its border.
@@ -24,7 +26,7 @@ Item {
 	/// Defaults to true if any corner has a non-zero radius, otherwise false.
 	property /*bool*/alias antialiasing: rectangle.antialiasing
 	/// The background color of the rectangle, which goes under its content.
-	property /*color*/alias color: shader.backgroundColor
+	property color color: "white"
 	/// See @@QtQuick.Rectangle.border.
 	property clippingRectangleBorder border
 	/// Radius of all corners. Defaults to 0.
@@ -70,19 +72,14 @@ Item {
 			anchors.fill: parent
 			anchors.margins: root.contentInsideBorder ? root.border.width : 0
 		}
-	}
 
-	ShaderEffect {
-		id: shader
-		anchors.fill: root
-		fragmentShader: `qrc:/Quickshell/Widgets/shaders/cliprect${root.contentUnderBorder ? "-ub" : ""}.frag.qsb`
-		property Rectangle rect: rectangle
-		property color backgroundColor: "white"
-		property color borderColor: root.border.color
-
-		property ShaderEffectSource content: ShaderEffectSource {
-			hideSource: true
-			sourceItem: contentItemContainer
+		layer.enabled: true
+		layer.samplerName: "content"
+		layer.effect: ShaderEffect {
+			fragmentShader: `qrc:/Quickshell/Widgets/shaders/cliprect${root.contentUnderBorder ? "-ub" : ""}.frag.qsb`
+			property Rectangle rect: rectangle
+			property color backgroundColor: root.color
+			property color borderColor: root.border.color
 		}
 	}
 }