SPV: Add OpSource shader source code and file name.

Test/spv.debugInfo.frag

@@ -0,0 +1,22 @@
+#version 450
+
+struct S {
+    int a;
+};
+
+uniform ubuf {
+    S s;
+};
+
+layout(location = 0) in vec4 inv;
+layout(location = 0) out vec4 outv;
+
+void foo(S s)
+{
+    outv = s.a * inv;
+}
+
+void main()
+{
+    foo(s);
+}