core/state: access trie through Database interface, track errors (#14589)

With this commit, core/state's access to the underlying key/value database is
mediated through an interface. Database errors are tracked in StateDB and
returned by CommitTo or the new Error method.

Motivation for this change: We can remove the light client's duplicated copy of
core/state. The light client now supports node iteration, so tracing and storage
enumeration can work with the light client (not implemented in this commit).

core/chain_makers.go

@@ -181,7 +181,7 @@ func GenerateChain(config *params.ChainConfig, parent *types.Block, db ethdb.Dat
 			gen(i, b)
 		}
 		ethash.AccumulateRewards(statedb, h, b.uncles)
-		root, err := statedb.Commit(config.IsEIP158(h.Number))
+		root, err := statedb.CommitTo(db, config.IsEIP158(h.Number))
 		if err != nil {
 			panic(fmt.Sprintf("state write error: %v", err))
 		}
@@ -189,7 +189,7 @@ func GenerateChain(config *params.ChainConfig, parent *types.Block, db ethdb.Dat
 		return types.NewBlock(h, b.txs, b.uncles, b.receipts), b.receipts
 	}
 	for i := 0; i < n; i++ {
-		statedb, err := state.New(parent.Root(), db)
+		statedb, err := state.New(parent.Root(), state.NewDatabase(db))
 		if err != nil {
 			panic(err)
 		}