Add support for VK_EXT_fragment_shader_barycentric

Test/spv.fragmentShaderBarycentric4.frag

@@ -0,0 +1,15 @@
+#version 320 es
+#extension GL_EXT_fragment_shader_barycentric : require
+
+precision highp float;
+
+layout(location = 0) pervertexEXT in float vertexIDs[3];
+      
+layout(location = 1) out float value;
+      
+void main () {
+    value = (gl_BaryCoordNoPerspEXT.x * vertexIDs[0] +
+             gl_BaryCoordNoPerspEXT.y * vertexIDs[1] +
+             gl_BaryCoordNoPerspEXT.z * vertexIDs[2]);
+
+}