Make DataFlowAnalyzer aware of storage / memory slot after sload / mload.

test/libyul/yulOptimizerTests/loadResolver/multi_sload_loop.yul

@@ -0,0 +1,30 @@
+{
+    let x := calldataload(0)
+    let len := sload(x)
+    let sum
+    for { let i := 0} lt(i, sload(x)) { i := add(i, 1) } {
+        let p := add(x, add(i, 1))
+        if gt(p, sload(x)) { revert(0, 0) }
+        sum := add(sum, sload(p))
+    }
+    mstore(0, sum)
+    return(0, 0x20)
+}
+// ----
+// step: loadResolver
+//
+// {
+//     let _1 := 0
+//     let x := calldataload(_1)
+//     let len := sload(x)
+//     let sum
+//     let i := _1
+//     for { } lt(i, len) { i := add(i, 1) }
+//     {
+//         let p := add(add(x, i), 1)
+//         if gt(p, len) { revert(_1, _1) }
+//         sum := add(sum, sload(p))
+//     }
+//     mstore(_1, sum)
+//     return(_1, 0x20)
+// }