Add missing d_bg_* TUs (#3058)

* Implement d_bg_s_capt_poly

* Add d_bg_s_func

* Ad d_bg_w_deform

* Add empty source file for d_bg_w_hf

src/d/d_bg_w_deform.cpp

@@ -0,0 +1,7 @@
+#include "d/dolzel.h" // IWYU pragma: keep
+
+static void dummy() {
+    ((J3DModel*)NULL)->offFlag(0);
+    ((J3DModel*)NULL)->onFlag(0);
+    ((J3DVertexBuffer*)NULL)->getCurrentVtxPos();
+}