add support for running pre-migrations and caching their results

This can significantly speedup state migrations.

node/builder.go

@@ -269,7 +269,7 @@ func Online() Option {
 			Override(new(vm.SyscallBuilder), vm.Syscalls),
 			Override(new(*store.ChainStore), modules.ChainStore),
 			Override(new(stmgr.UpgradeSchedule), stmgr.DefaultUpgradeSchedule()),
-			Override(new(*stmgr.StateManager), stmgr.NewStateManagerWithUpgradeSchedule),
+			Override(new(*stmgr.StateManager), modules.StateManager),
 			Override(new(*wallet.LocalWallet), wallet.NewWallet),
 			Override(new(wallet.Default), From(new(*wallet.LocalWallet))),
 			Override(new(api.WalletAPI), From(new(wallet.MultiWallet))),