Add examples for ORD()

[dveeden]

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Closes #16941

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[dveeden]

Maybe we should add more info about the difference between ORD() and ASCII()?

mysql> SELECT ORD('e'), ORD('ë'), ASCII('e'), ASCII('ë'), HEX('e'), HEX('ë');
+----------+-----------+------------+-------------+----------+-----------+
| ORD('e') | ORD('ë')  | ASCII('e') | ASCII('ë')  | HEX('e') | HEX('ë')  |
+----------+-----------+------------+-------------+----------+-----------+
|      101 |     50091 |        101 |         195 | 65       | C3AB      |
+----------+-----------+------------+-------------+----------+-----------+
1 row in set (0.00 sec)

[Oreoxmt]

@dveeden Could you please invite a tech reviewer? Thanks!

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[qiancai]

Rest LGTM

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[LGTM Timeline notifier]

Timeline:

• 2024-04-19 07:47:17.82959202 +0000 UTC m=+583456.940638470: ☑️ agreed by qiancai.
• 2024-04-22 09:26:25.045074526 +0000 UTC m=+848604.156120975: ☑️ agreed by hfxsd.

[qiancai]

/approve

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.0: #17312.