Speed up compilation of tst_qgraphicsview_2.cpp

Turn the list of newRow() calls into a for loop over a constexpr
data structure.

Fixes the GCC note:

   tst_qgraphicsview_2.cpp:47:13: note: variable tracking size limit exceeded with -fvar-tracking-assignments, retrying without

and speeds up compilation of the file from 13s to 2.5s on my
machine.

Task-number: QTBUG-38890
Change-Id: I4f0b3565c7df64b286d1d32eb3f3d6bf4df92609
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

tests/auto/widgets/graphicsview/qgraphicsview/tst_qgraphicsview.h

@@ -34,7 +34,7 @@
 // value to add/remove has to be obtained in test run using the actual style.
 
 struct ExpectedValueDescription {
-    ExpectedValueDescription(int v = 0, int sbeta = 0, int sta = 0)
+    Q_DECL_CONSTEXPR ExpectedValueDescription(int v = 0, int sbeta = 0, int sta = 0)
         : value(v)
         , scrollBarExtentsToAdd(sbeta)
         , spacingsToAdd(sta)
@@ -55,7 +55,7 @@ struct ExpectedValueDescription {
 // Describes how often the scroll bar width/height has to be added to/removed
 // from the according side of the sceneRect.
 struct ScrollBarCount {
-    ScrollBarCount(int l = 0, int t = 0, int r = 0, int b = 0 )
+    Q_DECL_CONSTEXPR ScrollBarCount(int l = 0, int t = 0, int r = 0, int b = 0 )
         : left(l)
         , top(t)
         , right(r)