Added a few optimizer tests for Verbatim

test/libyul/yulOptimizerTests/unusedPruner/verbatim.yul

@@ -0,0 +1,17 @@
+{
+    // cannot be removed because of verbatim
+    let a := mload(10)
+    // cannot be removed because of verbatim
+    let b := keccak256(10, 32)
+    // can be removed
+    let c := add(a, b)
+    verbatim_0i_0o("test")
+}
+// ----
+// step: unusedPruner
+//
+// {
+//     pop(mload(10))
+//     pop(keccak256(10, 32))
+//     verbatim_0i_0o("test")
+// }