vrend,feat: check for GL_OES_draw_buffers_indexed on GLES < 3.2

This helps expose GL_EXT_draw_buffers_indexed in the guest when the
host is not GLES 3.2 but provides the extension.

Enables tests
  dEQP-GLES31.functional.draw_buffers_indexed.random.
    max_required_draw_buffers.*

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>

src/vrend_renderer.c

@@ -178,8 +178,8 @@ static const  struct {
    [feat_gles31_vertex_attrib_binding] = { 43, 31, { "GL_ARB_vertex_attrib_binding" } },
    [feat_gpu_shader5] = { 40, 32, {"GL_ARB_gpu_shader5", "GL_EXT_gpu_shader5", "GL_OES_gpu_shader5" } },
    [feat_images] = { 42, 31, { "GL_ARB_shader_image_load_store" } },
-   [feat_indep_blend] = { 30, 32, { "GL_EXT_draw_buffers2" } },
-   [feat_indep_blend_func] = { 40, 32, { "GL_ARB_draw_buffers_blend" } },
+   [feat_indep_blend] = { 30, 32, { "GL_EXT_draw_buffers2", "GL_OES_draw_buffers_indexed" } },
+   [feat_indep_blend_func] = { 40, 32, { "GL_ARB_draw_buffers_blend", "GL_OES_draw_buffers_indexed"} },
    [feat_indirect_draw] = { 40, 31, { "GL_ARB_draw_indirect" } },
    [feat_mesa_invert] = { UNAVAIL, UNAVAIL, { "GL_MESA_pack_invert" } },
    [feat_ms_scaled_blit] = { UNAVAIL, UNAVAIL, { "GL_EXT_framebuffer_multisample_blit_scaled" } },