mesa: restore call to _mesa_set_varying_vp_inputs from set_vertex_processing_mode

Otherwise ctx->VertexProgram._VaryingInputs might not be up to date.

We can't do this in update_program because this breaks vbo_save_playback_vertex_list_gallium:

  const GLbitfield enabled = node->enabled_attribs[mode];
  _mesa_set_varying_vp_inputs(ctx, enabled);              <-- update _VaryingInputs

  if (ctx->NewState)
     _mesa_update_state(ctx);                             <-- calls update_program, reverting the
                                                              change made above

Fixes: c97961a855 ("mesa: fix 38% decrease in display list performance of Viewperf2020/NX8_StudioAA")
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/9441
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25956>

src/mesa/main/state.c

@@ -687,6 +687,9 @@ set_vertex_processing_mode(struct gl_context *ctx, gl_vertex_processing_mode m)
    default:
       assert(0);
    }
+
+   _mesa_set_varying_vp_inputs(ctx, ctx->VertexProgram._VPModeInputFilter &
+                               ctx->Array._DrawVAO->_EnabledWithMapMode);
 }