[YulOpt] Implement loop-invariant code motion

test/libyul/yulOptimizerTests/loopInvariantCodeMotion/dependOnVarInLoop.yul

@@ -0,0 +1,23 @@
+{
+  let b := 1
+  for { let a := 1 } iszero(eq(a, 10)) { a := add(a, 1) } {
+    let c := mload(3)    // c cannot be moved because non-movable
+    let not_inv := add(b, c) // no_inv cannot be moved because its value depends on c
+    a := add(a, 1)
+    mstore(a, not_inv)
+  }
+}
+// ====
+// step: loopInvariantCodeMotion
+// ----
+// {
+//     let b := 1
+//     let a := 1
+//     for { } iszero(eq(a, 10)) { a := add(a, 1) }
+//     {
+//         let c := mload(3)
+//         let not_inv := add(b, c)
+//         a := add(a, 1)
+//         mstore(a, not_inv)
+//     }
+// }