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/dump.go

@@ -41,7 +41,7 @@ type Dump struct {
 
 func (self *StateDB) RawDump() Dump {
 	dump := Dump{
-		Root:     common.Bytes2Hex(self.trie.Root()),
+		Root:     fmt.Sprintf("%x", self.trie.Hash()),
 		Accounts: make(map[string]DumpAccount),
 	}