Add support for WGSL

tests/syntax-tests/highlighted/WGSL/test.wgsl

@@ -0,0 +1,20 @@
+struct VertexOut {
+  @builtin(position) position : vec4f,
+  @location(0) color : vec4f
+}
+
+@vertex
+fn vertex_main(@location(0) position: vec4f,
+               @location(1) color: vec4f) -> VertexOut
+{
+  var output : VertexOut;
+  output.position = position;
+  output.color = color;
+  return output;
+}
+
+@fragment
+fn fragment_main(fragData: VertexOut) -> @location(0) vec4f
+{
+  return fragData.color;
+}