SPV: Implement new extensions GL_KHX_device_group and GL_KHX_multiview.

These correspond to SPV_KHR_device_group and SPV_KHR_multiview.
Also, bring tests up to date with Khronos internals, and some misc. related changes.

Test/spv.drawParams.vert

@@ -0,0 +1,13 @@
+#version 450
+
+#extension GL_ARB_shader_draw_parameters : enable
+
+out vec3 pos;
+
+void main()
+{
+    int a = gl_BaseVertexARB;
+    int b = gl_BaseInstanceARB;
+    int c = gl_DrawIDARB;
+    pos = vec3(a, b, c);
+}