Preserve redo log for mutable objects

Replay it during time travel debugging

src/runtime/set.js

@@ -0,0 +1,44 @@
+import {Multiversion, wrap_methods, rollback_if_needed} from './multiversion.js'
+
+export const defineMultiversionSet = window => {
+
+  // We declare class in such a weird name to have its displayed name to be
+  // exactly 'Set'
+  window.MultiversionSet = class Set extends window.Set {
+    
+    constructor(initial, cxt) {
+      super()
+      this.multiversion = new Multiversion(cxt)
+      this.initial = new globalThis.Set(initial)
+      this.redo_log = []
+      this.apply_initial()
+    }
+
+    apply_initial() {
+      super.clear()
+      for (const item of this.initial) {
+        super.add(item)
+      }
+    }
+
+    get size() {
+      rollback_if_needed(this)
+      return super.size
+    }
+
+  }
+
+  wrap_methods(
+    window.MultiversionSet,
+
+    // all methods
+    [
+      'has', 'add', 'delete', 'clear', 'entries', 'forEach', 'values', 'keys',
+      Symbol.iterator,
+    ],
+
+    // mutation methods
+    ['add', 'delete', 'clear'],
+  )
+
+}