fix broken service name "com.sun.star.rendering.VCLCanvas"

The service is actually called "com.sun.star.rendering.Canvas.VCL"
It looks like the code in SidebarPanel is a copy'n'paste from
PresenterHelper, and it looks like the PresenterHelper code has been
broken since 2008.

Change-Id: I78a0fa3bf9333d6473a743cffdb1dc41a7a1266d

sd/source/ui/presenter/PresenterHelper.cxx

@@ -215,7 +215,7 @@ Reference<rendering::XCanvas> SAL_CALL PresenterHelper::createCanvas (
             xFactory->createInstanceWithArguments(
                 !rsOptionalCanvasServiceName.isEmpty()
                     ? rsOptionalCanvasServiceName
-                    : OUString("com.sun.star.rendering.VCLCanvas"),
+                    : OUString("com.sun.star.rendering.Canvas.VCL"),
                 aArg),
             UNO_QUERY);
     }

sfx2/source/sidebar/SidebarPanel.cxx

@@ -105,7 +105,7 @@ cssu::Reference<css::rendering::XCanvas> SAL_CALL SidebarPanel::getCanvas (void)
         const ::comphelper::ComponentContext aComponentContext (::comphelper::getProcessServiceFactory());
         mxCanvas = Reference<rendering::XCanvas>(
             aComponentContext.createComponentWithArguments(
-                "com.sun.star.rendering.VCLCanvas",
+                "com.sun.star.rendering.Canvas.VCL",
                 aArg),
             UNO_QUERY);
     }