Add option to reflect all block members, inactive or active.

* The stages mask is more fine-grained, and each variable or block's mask
  indicates which stages it's active in.

Test/reflection.linked.frag

@@ -0,0 +1,19 @@
+#version 440 core
+
+layout(binding = 0, std140) uniform ubo_block {
+	float unused_uniform;
+	float shared_uniform;
+	float vsonly_uniform;
+	float fsonly_uniform;
+} ubo;
+
+in float vertout;
+
+out float fragout;
+
+void main()
+{
+    fragout = vertout;
+    fragout += ubo.shared_uniform;
+    fragout += ubo.fsonly_uniform;
+}