wgl: Fix depth/stencil image support when using zink kopper
What does this MR do and why?
Kopper requires that any depth/stencil images are created through winsys which was not taken into account by the WGL frontend causing it to hit an assert: 'Assertion failed: ctx->fb_state.zsbuf->texture->bind & PIPE_BIND_DISPLAY_TARGET'
fixes #9256 (closed)