Add "roundVector" function as convenience for rounding a QVector2D

Otherwise we constantly need to construct and deconstruct vectors.

src/libkwineffects/kwineffects.h

@@ -38,6 +38,7 @@
 #include <netwm.h>
 
 #include <climits>
+#include <cmath>
 #include <functional>
 #include <optional>
 
@@ -196,6 +197,14 @@ KWINEFFECTS_EXPORT inline QRectF scaledRect(const QRectF &rect, qreal scale)
     return QRectF{rect.x() * scale, rect.y() * scale, rect.width() * scale, rect.height() * scale};
 }
 
+/**
+ * Round a vector to nearest integer.
+ */
+KWINEFFECTS_EXPORT inline QVector2D roundVector(const QVector2D &input)
+{
+    return QVector2D(std::round(input.x()), std::round(input.y()));
+}
+
 /**
  * @short Base class for all KWin effects
  *