Online DDL: recognize shorter vitess artifact table name

[shlomi-noach]

Description

Initial support for #14570. This PR merely recognizes this new shorter naming scheme as an OnlineDDL table name, .e.g _4e5dcf80_354b_11eb_82cd_f875a4d24e90_20201203114013_vrp.

This name is two characters shorter than the current scheme (e.g. _4e5dcf80_354b_11eb_82cd_f875a4d24e90_20201203114013_vrepl). It allows default constraint names with one or two digits. For example:

mysql> create table _84371a37_6153_11eb_9917_f875a4d24e90_20210128122816_vrp(id int primary key, pid int, foreign key (pid) references p(id));
Query OK, 0 rows affected (0.06 sec)

mysql> show create table _84371a37_6153_11eb_9917_f875a4d24e90_20210128122816_vrp\G
*************************** 1. row ***************************
       Table: _84371a37_6153_11eb_9917_f875a4d24e90_20210128122816_vrp
Create Table: CREATE TABLE `_84371a37_6153_11eb_9917_f875a4d24e90_20210128122816_vrp` (
  `id` int NOT NULL,
  `pid` int DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `pid` (`pid`),
  CONSTRAINT `_84371a37_6153_11eb_9917_f875a4d24e90_20210128122816_vrp_ibfk_1` FOREIGN KEY (`pid`) REFERENCES `p` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci

The name _84371a37_6153_11eb_9917_f875a4d24e90_20210128122816_vrp_ibfk_1 is 63 characters long, and thus we can support up to _84371a37_6153_11eb_9917_f875a4d24e90_20210128122816_vrp_ibfk_99 with this naming scheme.

This PR only accepts this new naming scheme. A followup PR will actually use it.

Related Issue(s)

#14570

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on the CI
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

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[deepthi]

Leaving this to @shlomi-noach to merge or not (based on further developments / learnings on the topic).

[shlomi-noach]

On hold while we debate #14582

[shlomi-noach]

Closed in favor of #14613