wxOSX Retina fixes: size wxStaticBitmap and wxBitmapButton properly.

The size is expressed in logical coordinates and needs to use bitmap's
scaled size, otherwise it would appear twice as large in both
dimensions.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75348 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
wxOSX Retina fixes: wxImageList::GetSize().

wxImageList returns size of its bitmap as pixel size, i.e.  twice the
displayed screen on HiDPI screens.  Unfortunately,
wxImageList::GetSize() is used heavily in (generic) GUI drawing code,
e.g.  to properly size wxListCtrl's icon columns.  As wxImageList is
used primarily by controls, it seems reasonable to adjust for scaling
here, rather than requiring all users of the class to do it.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75349 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775