vcl: add initializer_list constructor to BitmapPalette and use it

Change-Id: Ib24266e435765bd5e05193aea5cee61d7a9346b0
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/113133
Tested-by: Jenkins
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>

cppcanvas/source/mtfrenderer/implrenderer.cxx

@@ -202,9 +202,9 @@ namespace
                               const ::Color& rMaskColor )
     {
         const ::Color aWhite( COL_WHITE );
-        BitmapPalette aBiLevelPalette(2);
-        aBiLevelPalette[0] = aWhite;
-        aBiLevelPalette[1] = rMaskColor;
+        BitmapPalette aBiLevelPalette{
+            aWhite, rMaskColor
+        };
 
         Bitmap aMask( rBitmap.CreateMask( aWhite ));
         Bitmap aSolid( rBitmap.GetSizePixel(),