buildValuesListOfInsert is slow when many ‘?’ in values

[lysu]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

use prepare to execute

insert into t values(?, ?, ?), (?, ?, ?), (?, ?, ?), (?, ?, ?), (?, ?, ?), (?, ?, ?), (?, ?, ?), (?, ?, ?), (?, ?, ?), (?, ?, ?), (?, ?, ?), (?, ?, ?).....

2. What did you expect to see? (Required)

fast and low cpu usage in tidb

3. What did you see instead (Required)

hig cpu usage

it seems rewrite for each "?" is unessary

4. What is your TiDB version? (Required)

v5.0.0 (previous flamegraph's code line number is also v5.0.0.)