other preload microoptimizations

Summary:
make svgitem schedule a polish right when it's done loading

ScrollView now forces to layout items as soon is created, to preload items
before the window is shown

remove useless include

Test Plan:
possible to preload (almost) the whole systray with less hacks
on that part (see D10692)

Reviewers: #plasma, davidedmundson, broulik

Reviewed By: #plasma, broulik

Subscribers: davidedmundson, broulik, plasma-devel, #frameworks

Tags: #plasma, #frameworks

Differential Revision: https://phabricator.kde.org/D10722

src/declarativeimports/plasmaextracomponents/qml/ScrollArea.qml

@@ -51,5 +51,13 @@ QtQuickControls.ScrollView {
         }
         contentItem.focus = true
     }
+    //we want plasmoid popups open as quick as possible at start.
+    //this makes sure things with big list views (kickoff, clipboard)
+    //are loaded when created, even before they are shown
+    Component.onCompleted: {
+        if (typeof contentItem.forceLayout === "function") {
+            contentItem.forceLayout();
+        }
+    }
     //end hack
 }