MDEV-38046 Make func_regexp_pcre tolerant to PCRE2 offset change

[aquilamacedo]

PCRE2 10.47 reports the invalid escape in 'A\q' at offset 3 instead of 2. Update the expected result and add a --replace_regex in the test so the suite passes with both older and newer PCRE2 versions.

• The Jira issue number for this PR is: MDEV-38046

Description

PCRE2 10.47 tightened/improved its error reporting and now points one character further into the pattern when it encounters an invalid escape such as \q. The test main.func_regexp_pcre was asserting on the literal error text coming back from PCRE2:

ERROR 42000: Regex error 'unrecognized character follows \ at offset 2'

With PCRE2 10.47 this becomes:

ERROR 42000: Regex error 'unrecognized character follows \ at offset 3'

This made the test brittle across PCRE2 versions.

This patch does two things:

1. Updates mysql-test/main/func_regexp_pcre.result to the newer wording (offset 3) produced by PCRE2 10.47.
2. Adds a --replace_regex /offset 2/offset 3/ to mysql-test/main/func_regexp_pcre.test right before the failing statement, so older PCRE2 that still reports offset 2 will be normalized to offset 3 during test run.

That way the same test can pass with both older and newer PCRE2 without changing server code.

There should be no side effects for runtime behaviour: this only relaxes the test harness around version-dependent diagnostic text.

Release Notes

Adjusts regex test to accept PCRE2 10.47's updated error offset message.

How can this PR be tested?

1. Use a system with PCRE2 10.47 (e.g. Debian experimental which currently ships it).

2. Build MariaDB server against that PCRE2.

3. Run:

   mysql-test-run.pl main.func_regexp_pcre

If the test passes both with older PCRE2 (offset 2) and with 10.47+ (offset 3), the change works.

Basing the PR against the correct MariaDB version

• This is a new feature or a refactoring, and the PR is based against the main branch.
• This is a bug fix, and the PR is based against the earliest maintained branch in which the bug can be reproduced.

PR quality check

• I checked the CODING_STANDARDS.md file and my PR conforms to this where appropriate.
• For any trivial modifications to the PR, I am ok with the reviewer making the changes themselves.

[NWilson]

🚀 Looks good to me as PCRE2 maintainer.

(And - my thanks again for coping with this bit of churn from us. I try very hard for PCRE2 releases to be drop-in compatible with minimal behavioural changes, and I'm sorry this impacted you.)