Fix conversion of bitmaps with alpha to icons/cursors in wxMSW.

Fix conversion of bitmaps with alpha to icons/cursors in wxMSW.

CreateIconIndirect() applies pre-multiplication to the bitmap itself (as can be
seen by experimenting with this or reading WINE sources for it) and so we must
pass it a bitmap with data in non-pre-multiplied format to avoid doing it
twice.

This is similar to the change to wxImageList in the previous commit, see #9050.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65961 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775