Remove manual mirroring in RTL case from wxGrid code.

This is not necessary as wxDC already inherits RTL from the window itself and,
in fact, breaks the display when using RTL.

Closes #16250.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77038 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Link wxMSW with msimg32.lib now that AlphaBlend() is used statically.

Implicitly link msimg32.lib in when using MSVC and add it to MinGW (and
Borland) makefiles.

This should have been part of r77029.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77039 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775