Add more tests for future changes

tests/push_constants/push_constant_basic_0.glsl

@@ -0,0 +1,23 @@
+#version 460
+#extension GL_EXT_buffer_reference : enable
+
+layout(buffer_reference) buffer Node { uint x; };
+
+struct Bar {
+    uint t;
+    uint s;
+};
+
+layout(push_constant, std430) uniform foo {
+    uint a;
+    uint b[4];
+    Bar bar;
+    Node node;
+};
+
+layout(set=0, binding=0) buffer SSBO {
+    uint out_value;
+};
+
+// Everything should be marked as UNUSED
+void main() {}