Add function side effects test.

test/libyul/functionSideEffects/verbatim.yul

@@ -0,0 +1,8 @@
+{
+    function a() -> x { x := verbatim_0i_1o(hex"6007") }
+    function b() { let t := a() }
+}
+// ----
+// : movable, movable apart from effects, can be removed, can be removed if no msize
+// a: can loop, writes other state, writes storage, writes memory
+// b: can loop, writes other state, writes storage, writes memory