MDEV-35309 - ALTER performs vector truncation without WARN_DATA_TRUNCATED or similar warnings/errors

[svoj]

• The Jira issue number for this PR is: MDEV-35309

Description

Let ALTER TABLE issue a warning/error when VECTOR data is truncated, but only if tail has meaningful (non-zero) values.

Release Notes

How can this PR be tested?

mtr vector2

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.

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