Fix visitation order bug for structural simplifier.

test/libyul/yulOptimizerTests/structuralSimplifier/bugfix_visit_after_change.yul

@@ -0,0 +1,13 @@
+{
+	// This tests that a bug is fixed where x := 1 was wrongfully
+	// taken into account before actually visiting the if statement.
+	let x := 0
+	if x {
+		x := 1
+	}
+}
+// ----
+// structuralSimplifier
+// {
+//     let x := 0
+// }

test/libyul/yulOptimizerTests/structuralSimplifier/switch_no_remove_empty_case.yul

@@ -1,6 +1,6 @@
 {
 	let y := 200
-	switch y
+	switch calldataload(0)
 	case 0 { }
 	case 1 { y := 9 }
 	default { y := 100 }
@@ -9,7 +9,7 @@
 // structuralSimplifier
 // {
 //     let y := 200
-//     switch y
+//     switch calldataload(0)
 //     case 0 {
 //     }
 //     case 1 {