MDEV-35152 - DATA/INDEX DIRECTORY options are ignored for vector index

[svoj]

• The Jira issue number for this PR is: MDEV-35152

Description

Let high-level indexes honor DATA/INDEX DIRECTORY table options: now they store high-level index data files in DATA DIRECTORT and index files in INDEX DIRECTORY.

How can this PR be tested?

mtr vector_symlink

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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