Doc: Add example category to all the files that haven't yet got it

Added example category and also fixed one copy-paste mistake in Vulkan Texture Import.

Task-number: QTBUG-116205
Change-Id: I96692f214849596e9555c635d9996d9b884c5cab
Reviewed-by: Kai Köhne <kai.koehne@qt.io>
(cherry picked from commit e421c21c3b)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

examples/quick/scenegraph/customgeometry/doc/src/customgeometry.qdoc

@@ -4,6 +4,7 @@
 /*!
     \example scenegraph/customgeometry
     \title Scene Graph - Custom Geometry
+    \examplecategory {Graphics & Multimedia}
     \ingroup qtquickexamples
     \brief Shows how to implement a custom geometry in the Qt Quick Scene Graph.
 

examples/quick/scenegraph/custommaterial/doc/src/custommaterial.qdoc

@@ -4,6 +4,7 @@
 /*!
     \example scenegraph/custommaterial
     \title Scene Graph - Custom Material
+    \examplecategory {Graphics & Multimedia}
     \ingroup qtquickexamples
     \brief Shows how to implement a custom material in the Qt Quick Scene Graph.
 

examples/quick/scenegraph/customrendernode/doc/src/customrendernode.qdoc

@@ -4,6 +4,7 @@
 /*!
     \example scenegraph/customrendernode
     \title Scene Graph - Custom QSGRenderNode
+    \examplecategory {Graphics & Multimedia}
     \ingroup qtquickexamples
     \brief Shows how to use QSGRenderNode to implement custom rendering in the Qt Quick scenegraph.
 

examples/quick/scenegraph/d3d11underqml/doc/src/d3d11underqml.qdoc

@@ -4,6 +4,7 @@
 /*!
     \example scenegraph/d3d11underqml
     \title Scene Graph - Direct3D 11 Under QML
+    \examplecategory {Graphics & Multimedia}
     \ingroup qtquickexamples
     \brief Shows how to render directly with Direct3D 11 under a Qt Quick scene.
 

examples/quick/scenegraph/graph/doc/src/graph.qdoc

@@ -4,6 +4,7 @@
 /*!
     \example scenegraph/graph
     \title Scene Graph - Graph
+    \examplecategory {Graphics & Multimedia}
     \ingroup qtquickexamples
 
     \brief Demonstrates how one can combine custom materials and geometries

examples/quick/scenegraph/metaltextureimport/doc/src/metaltextureimport.qdoc

@@ -4,6 +4,7 @@
 /*!
     \example scenegraph/metaltextureimport
     \title Scene Graph - Metal Texture Import
+    \examplecategory {Graphics & Multimedia}
     \ingroup qtquickexamples
     \brief Shows how to use a texture created directly with Metal.
 

examples/quick/scenegraph/metalunderqml/doc/src/metalunderqml.qdoc

@@ -4,6 +4,7 @@
 /*!
     \example scenegraph/metalunderqml
     \title Scene Graph - Metal Under QML
+    \examplecategory {Graphics & Multimedia}
     \ingroup qtquickexamples
     \brief Shows how to render directly with Metal under a Qt Quick scene.
 

examples/quick/scenegraph/openglunderqml/doc/src/openglunderqml.qdoc

@@ -4,6 +4,7 @@
 /*!
     \example scenegraph/openglunderqml
     \title Scene Graph - OpenGL Under QML
+    \examplecategory {Graphics & Multimedia}
     \ingroup qtquickexamples
     \brief Shows how to render OpenGL under a Qt Quick scene.
 

examples/quick/scenegraph/rhitextureitem/doc/src/rhitextureitem.qdoc

@@ -4,6 +4,7 @@
 /*!
     \example scenegraph/rhitextureitem
     \title Scene Graph - RHI Texture Item
+    \examplecategory {Graphics & Multimedia}
     \ingroup qtquickexamples
 
     \brief Shows how to implement a custom QQuickItem that displays a QRhi-rendered texture.

examples/quick/scenegraph/rhiunderqml/doc/src/rhiunderqml.qdoc

@@ -4,6 +4,7 @@
 /*!
     \example scenegraph/rhiunderqml
     \title Scene Graph - RHI Under QML
+    \examplecategory {Graphics & Multimedia}
     \ingroup qtquickexamples
     \brief Shows how to render directly with \l QRhi under a Qt Quick scene.
 

examples/quick/scenegraph/twotextureproviders/doc/src/twotextureproviders.qdoc

@@ -4,6 +4,7 @@
 /*!
     \example scenegraph/twotextureproviders
     \title Scene Graph - Two Texture Providers
+    \examplecategory {Graphics & Multimedia}
     \ingroup qtquickexamples
 
     \brief Shows how to combine two textures from two texture providers in a custom scene graph node.

examples/quick/scenegraph/vulkantextureimport/doc/src/vulkantextureimport.qdoc

@@ -4,8 +4,9 @@
 /*!
     \example scenegraph/vulkantextureimport
     \title Scene Graph - Vulkan Texture Import
+    \examplecategory {Graphics & Multimedia}
     \ingroup qtquickexamples
-    \brief Shows how to use a texture created directly with use a texture created directly withulkan.
+    \brief Shows how to use a texture created directly with Vulkan.
 
     \image vulkantextureimport-example.jpg
 

examples/quick/scenegraph/vulkanunderqml/doc/src/vulkanunderqml.qdoc

@@ -4,6 +4,7 @@
 /*!
     \example scenegraph/vulkanunderqml
     \title Scene Graph - Vulkan Under QML
+    \examplecategory {Graphics & Multimedia}
     \ingroup qtquickexamples
     \brief Shows how to render directly with Vulkan under a Qt Quick scene.