reduce alloc costs for some basegfx objects (tdf#105575)

we can use a default object for the default constructo case, and
remove one malloc for each default constructed object

Change-Id: I0bec37ef9161a210973abb25669a9f16a5e0ea75
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/120603
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

basegfx/source/matrix/b2dhommatrix.cxx

@@ -31,7 +31,9 @@ namespace basegfx
     {
     };
 
-    B2DHomMatrix::B2DHomMatrix() = default;
+    static o3tl::cow_wrapper<Impl2DHomMatrix> DEFAULT;
+
+    B2DHomMatrix::B2DHomMatrix() : mpImpl(DEFAULT) {}
 
     B2DHomMatrix::B2DHomMatrix(const B2DHomMatrix&) = default;
 

basegfx/source/polygon/b2dpolypolygon.cxx

@@ -200,7 +200,10 @@ public:
 namespace basegfx
 {
 
-    B2DPolyPolygon::B2DPolyPolygon() = default;
+    static o3tl::cow_wrapper<ImplB2DPolyPolygon> DEFAULT;
+
+    B2DPolyPolygon::B2DPolyPolygon() :
+        mpPolyPolygon(DEFAULT) {}
 
     B2DPolyPolygon::B2DPolyPolygon(const B2DPolyPolygon&) = default;