vrend,features: Sample shading is provided by GLES 3.2

Also add OES_sample_shading to the test.

Fixes:
 dEQP-GLES31.functional.image_load_store.2d.format_reinterpret.rgba16i_rgba16f
 dEQP-GLES31.functional.image_load_store.2d.format_reinterpret.rgba32i_rgba32f
 dEQP-GLES31.functional.image_load_store.3d.format_reinterpret.r32ui_r32f
 dEQP-GLES31.functional.image_load_store.3d.format_reinterpret.rgba16ui_rgba16f
 dEQP-GLES31.functional.image_load_store.cube.format_reinterpret.r32ui_r32f

Enabled (with some failures):
 dEQP-GLES31.functional.debug.negative_coverage.*
 dEQP-GLES31.functional.sample_shading.* (with some failures)
 dEQP-GLES31.functional.shaders.sample_variables.*
 dEQP-GLES31.functional.shaders.multisample_interpolation.*

Closes: #3

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

src/vrend_renderer.c

@@ -187,7 +187,7 @@ static const  struct {
    [feat_polygon_offset_clamp] = { 46, UNAVAIL, { "GL_ARB_polygon_offset_clamp" } },
    [feat_robust_buffer_access] = { 43, UNAVAIL, { "GL_ARB_robust_buffer_access_behaviour" } },
    [feat_sample_mask] = { 32, 31, { "GL_ARB_texture_multisample" } },
-   [feat_sample_shading] = { 40, UNAVAIL, { "GL_ARB_sample_shading" } },
+   [feat_sample_shading] = { 40, 32, { "GL_ARB_sample_shading", "GL_OES_sample_shading" } },
    [feat_samplers] = { 33, 30, { "GL_ARB_sampler_objects" } },
    [feat_shader_clock] = { UNAVAIL, UNAVAIL, { "GL_ARB_shader_clock" } },
    [feat_ssbo] = { 43, 31, { "GL_ARB_shader_storage_buffer_object" } },