Utils: Add default ctors for Layouting::{Row,Column,Flow}

Helpful when filling a layout manually.

Change-Id: Id21a9ce1e280f999699529212a8bf713429524eb
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

src/libs/utils/layoutbuilder.cpp

@@ -626,6 +626,11 @@ void withFormAlignment(Layout *layout)
 
 // Flow
 
+Flow::Flow()
+{
+    ptr = new FlowLayout;
+}
+
 Flow::Flow(std::initializer_list<I> ps)
 {
     ptr = new FlowLayout;
@@ -633,7 +638,12 @@ Flow::Flow(std::initializer_list<I> ps)
     flush();
 }
 
-// Row & Column
+// Row
+
+Row::Row()
+{
+    ptr = new QHBoxLayout;
+}
 
 Row::Row(std::initializer_list<I> ps)
 {
@@ -642,6 +652,13 @@ Row::Row(std::initializer_list<I> ps)
     flush();
 }
 
+// Column
+
+Column::Column()
+{
+    ptr = new QVBoxLayout;
+}
+
 Column::Column(std::initializer_list<I> ps)
 {
     ptr = new QVBoxLayout;

src/libs/utils/layoutbuilder.h

@@ -155,6 +155,7 @@ public:
     using Implementation = QVBoxLayout;
     using I = Building::BuilderItem<Column>;
 
+    Column();
     Column(std::initializer_list<I> ps);
 };
 
@@ -164,6 +165,7 @@ public:
     using Implementation = QHBoxLayout;
     using I = Building::BuilderItem<Row>;
 
+    Row();
     Row(std::initializer_list<I> ps);
 };
 
@@ -190,6 +192,7 @@ public:
 class QTCREATOR_UTILS_EXPORT Flow : public Layout
 {
 public:
+    Flow();
     Flow(std::initializer_list<I> ps);
 };