Respect alignment flags for owner-drawn buttons in wxMSW.

Honour wxBU_{LEFT,RIGHT,TOP,BOTTOM} flags for owner drawn buttons too, this
ensures that you can both change the colour and align the text differently for
buttons under XP and later.

Closes #12995.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67184 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775