Doc: improve grabToImage snippets

- Change the code that is quoted so that the indenting looks sane
- Make it possible to copy and run the first snippet without
  modification
- Make it easier to copy and run the second snippet without
  modification
- Move itemGrab.qml to item sub-directory
- Generally tidy up

Pick-to: 6.2 6.4 6.5
Change-Id: I608b7a6025b9866c14b84420ae64827965a7519f
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

src/quick/doc/snippets/qml/item/itemGrab.qml

@@ -0,0 +1,39 @@
+// Copyright (C) 2014 Jolla Ltd, author: <gunnar.sletta@jollamobile.com>
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+import QtQuick 2.4
+
+Item {
+    width: 320
+    height: 480
+
+//! [grab-to-file]
+Rectangle {
+    id: sourceRectangle
+    width: 100
+    height: 100
+    gradient: Gradient {
+        GradientStop { position: 0; color: "steelblue" }
+        GradientStop { position: 1; color: "black" }
+    }
+
+    Component.onCompleted: {
+        sourceRectangle.grabToImage(function(result) {
+           result.saveToFile("something.png")
+        })
+    }
+}
+//! [grab-to-file]
+
+//! [grab-to-image]
+Image {
+    id: image
+}
+
+Component.onCompleted: {
+    sourceRectangle.grabToImage(function(result) {
+        image.source = result.url
+    }, Qt.size(50, 50))
+}
+//! [grab-to-image]
+}

src/quick/items/qquickitemgrabresult.cpp

@@ -345,17 +345,15 @@ QSharedPointer<QQuickItemGrabResult> QQuickItem::grabToImage(const QSize &target
  *
  * If the grab could not be initiated, the function returns \c false.
  *
- * The following snippet shows how to grab an item and store the results to
- * a file.
+ * The following snippet shows how to grab an item and store the results in
+ * a file:
  *
- * \snippet qml/itemGrab.qml grab-source
- * \snippet qml/itemGrab.qml grab-to-file
+ * \snippet qml/item/itemGrab.qml grab-to-file
  *
  * The following snippet shows how to grab an item and use the results in
- * another image element.
+ * another image element:
  *
- * \snippet qml/itemGrab.qml grab-image-target
- * \snippet qml/itemGrab.qml grab-to-cache
+ * \snippet qml/item/itemGrab.qml grab-to-image
  *
  * \note This function will render the item to an offscreen surface and
  * copy that surface from the GPU's memory into the CPU's memory, which can