function tokenize(tokenizer_name: string, content: string) -> list of strings

// input 
tokenizer_name: needs to be limited to the existing tokenizers. For now, only support chinese, english, standard.
content: text, but notice that the language corresponding to the text content only achieves the expected effect when work with the specified tokenizer.

// output 
tokens: splited and analyzed by tokenizer

// tokenize with english
mysql> SELECT tokenize('english', 'Today is saturday');
+------------------------------------------+
| tokenize('english', 'Today is saturday') |
+------------------------------------------+
| ["today","is","saturday"]                |
+------------------------------------------+
1 row in set (0.00 sec)

// count word frequency
mysql> select unnest, count(*) as count 
mysql> from t_tokenized_table, unnest(tokenize('english', english_text)) as unnest
mysql> group by unnest order by count;
+----------+-------+
| unnest   | count |
+----------+-------+
| world    |     1 |
| comes    |     1 |
| tap      |     1 |
| the      |     1 |
| from     |     1 |
| sea      |     1 |
| shanghai |     1 |
| water    |     1 |
| hello    |     2 |
+----------+-------+
9 rows in set (0.06 sec)