Fix font size when using wxGraphicsContext with wxPrinterDC in wxMSW.

Use pixel size which is scaled correctly by GDI+ itself instead of the size in
points which is currently not scaled correctly by wx.

Closes #3566.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@76008 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775