MDEV-35394 Innochecksum misinterprets freed undo pages

[Thirunarayanan]

• The Jira issue number for this PR is: MDEV-35394

Description

• Innochecksum misinterprets the freed undo log pages as active one. This leads the user to think there are too many undo log pages exist.

• Innochecksum can safely assume the undo log page is freed if the respective extent doesn't belong to a segment and marked as freed in XDES_BITMAP in extent descriptor page.

• Innochecksum shouldn't assume that zero-filled page as extent descriptor page.

How can this PR be tested?

./mtr innodb.innochecksum_undo_page

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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