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/state/managed_state_test.go

@@ -27,7 +27,7 @@ var addr = common.BytesToAddress([]byte("test"))
 
 func create() (*ManagedState, *account) {
 	db, _ := ethdb.NewMemDatabase()
-	statedb, _ := New(common.Hash{}, db)
+	statedb, _ := New(common.Hash{}, NewDatabase(db))
 	ms := ManageState(statedb)
 	ms.StateDB.SetNonce(addr, 100)
 	ms.accounts[addr] = newAccount(ms.StateDB.getStateObject(addr))