MDEV-9343 Copying from YEAR to DATE result in '0000-00-00'

[HazemRawi]

When converting YEAR values to DATE/DATETIME, explicitly set month and day to zero (e.g., 2000 → 2000-00-00). Validate against SQL modes:

• Allow 2000-00-00 if NO_ZERO_IN_DATE is disabled
• Reject if NO_ZERO_IN_DATE is enabled

• The Jira issue number for this PR is: MDEV-9343

Description

This fix explicitly targets YEAR to DATE or DATETIME conversions (setting month=0, day=0).
Queries involving YEAR(), MONTH(), or DAY() functions will change its behavior because they rely on the same conversion logic (number_to_datetime_or_date, str_to_datetime_or_date_body) used for date parsing.

Release Notes

The server now preserves the year value when converting YEAR to DATE or DATETIME, resulting in YYYY-00-00.

How can this PR be tested?

Run ./mtr main.type_date

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.

[HazemRawi]

Ping 👀

[svoj]

@HazemRawi Hi! This pull request was assigned to @abarkov for review. MDEV-9434 received Critical priority, which means it is constantly on radar.

In the meantime, please rebase on top of fresh 10.11, it contains fix for massive main.timezone failure. Also please check buildbot status, there're failures that are very likely caused by this patch.

[svoj]

As requested in the comment: rebase and check bb failures.