Adding test for deleting packed storage array.

test/libsolidity/semanticTests/array/delete_storage_array_packed.sol

@@ -0,0 +1,18 @@
+contract C {
+    uint120[] data;
+
+    function f() public returns (uint120, uint120, uint120) {
+        data.push(123);
+        data.push(234);
+        data.push(345);
+        delete data;
+        assembly {
+            sstore(data.slot, 3)
+        }
+        return (data[0], data[1], data[2]);
+    }
+}
+// ====
+// compileViaYul: also
+// ----
+// f() -> 0, 0, 0