test_index_buffer_offset() occasionally fails (on some machines and/or Mesa versions) due to a bug in radeonsi. Although the bug has since been fixed upstream, I ended up writing these patches for it, and since they reduce GL calls I'm inclined to believe they're a good idea regardless.
The relevant Mesa bug is https://gitlab.freedesktop.org/mesa/mesa/-/issues/6138.
-- v2: wined3d: Do not pause transform feedback after every draw call. wined3d: Pause transform feedback in wined3d_context_gl_draw_textured_quad(). wined3d: Pause transform feedback in wined3d_context_gl_draw_shaded_quad().