Improve Post-Meta handling

[pfefferle]

this is a follow up of #1821

Proposed changes:

• Do not store post-meta if empty or has the default value

Other information:

• Have you written new tests for your changes, if applicable?

Testing instructions:

• Go to '..'

Changelog entry

• Automatically create a changelog entry from the details below.

Changelog Entry Details

Significance

• Patch
• Minor
• Major

Type

• Added - for new features
• Changed - for changes in existing functionality
• Deprecated - for soon-to-be removed features
• Removed - for now removed features
• Fixed - for any bug fixes
• Security - in case of vulnerabilities

Message

Prevent storage of empty or default post meta values.

[Copilot]

Pull Request Overview

This PR prevents storing post-meta values when they are empty or match the default values. The key changes include updating test files to use nowdoc syntax for heredocs, replacing the previous actions with filters to intercept meta additions/updates, and implementing a new function to conditionally delete meta values.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/includes/class-test-mention.php	Switched heredoc to nowdoc syntax in test data.
tests/includes/class-test-link.php	Updated nowdoc syntax for style and pre blocks in test content.
tests/includes/class-test-hashtag.php	Updated nowdoc syntax for style and pre blocks in test content.
includes/class-activitypub.php	Replaced actions with filters and refactored meta handling logic.
.github/changelog/1829-from-description	Updated changelog entry to document the meta handling change.

[pfefferle]

@obenland all addressed in 034b01b