MDEV-38180: Added XXH3 and XXH32 (64 bit) sql functions

[AbhinavMishra32]

• The Jira issue number for this PR is: MDEV-38180

Description

Adds native SQL functions XXH32() and XXH3() exposing xxHash algorithms.

Release Notes

Added XXH32() and XXH3() SQL functions that return 32‑bit and 64‑bit xxHash digests (unsigned integers). NULL or empty input returns SQL NULL.

How can this PR be tested?

./mysql-test/mtr main.func_xxh

If the changes are not amenable to automated testing, please explain why not and carefully describe how to test manually.

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.

[CLAassistant]

All committers have signed the CLA.

[AbhinavMishra32]

@FooBarrior @mariadb-YuchenPei please review🙂

[gkodinov]

Thank you for your contribution!

This is a preliminary review.

Please consider filling up a complete specification of the function into the related jira. E.g.: How does it calculate the hash for various data types, how does collation matter for strings, type and number of arguments, nullability, expected data type etc.

Please also find one additional optional arguments suggestion below.

[gkodinov]

It looks like a wrong commit went in here.

Can we just please have the single commit?
And also some better description of the functions added?

[grooverdan]

@mariadb-YuchenPei tells me that since MDEV-9826 has been merged to main, this needs a full rebased onto main, which I've now done.