Enable GL_KHR_shader_subgroup properly

(and GL_NV_shader_subgroup_partitioned) based on GL/ES version
instead of predicating it on vulkan SPV generation

Also add AST testing.
The glsl.450.subgroup* files are largely the same as the spv.subgroup*
The glsl.es320.subgroup* files are the same as the 450 versions, but modified to be ES compatible.

Test/glsl.es320.subgroupBasic.comp

@@ -0,0 +1,23 @@
+#version 320 es
+
+#extension GL_KHR_shader_subgroup_basic: enable
+
+layout (local_size_x = 8, local_size_y = 8, local_size_z = 1) in;
+
+layout(binding = 0) buffer Buffer
+{
+    int a[];
+} data;
+
+void main()
+{
+    data.a[gl_SubgroupSize] = 1;
+    data.a[gl_SubgroupInvocationID] = 1;
+    data.a[gl_NumSubgroups] = 1;
+    data.a[gl_SubgroupID] = (subgroupElect()) ? 1 : 0;
+    subgroupBarrier();
+    subgroupMemoryBarrier();
+    subgroupMemoryBarrierBuffer();
+    subgroupMemoryBarrierShared();
+    subgroupMemoryBarrierImage();
+}