trie: add getter for preimage store in trie.Database (#28155)

trie/database.go

@@ -189,6 +189,15 @@ func (db *Database) WritePreimages() {
 	}
 }
 
+// Preimage retrieves a cached trie node pre-image from memory. If it cannot be
+// found cached, the method queries the persistent database for the content.
+func (db *Database) Preimage(hash common.Hash) []byte {
+	if db.preimages == nil {
+		return nil
+	}
+	return db.preimages.preimage(hash)
+}
+
 // Cap iteratively flushes old but still referenced trie nodes until the total
 // memory usage goes below the given threshold. The held pre-images accumulated
 // up to this point will be flushed in case the size exceeds the threshold.