Strip whitespace between HTML tags instead of all content

[pfefferle]

Fixes #2592 Supersedes #2595

Proposed changes:

• Add Sanitize::strip_whitespace() method that only removes newlines, carriage returns, and tabs between HTML tags (/>[\n\r\t]+</) rather than stripping them from all content.
• This preserves whitespace inside preformatted elements like <pre> and <code> blocks without needing special handling.
• Update Shortcodes::content() to use the new sanitization method.
• Remove redundant wpautop() and whitespace stripping from Post::get_content() since content is already processed.

Other information:

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

Testing instructions:

1. Create a post with a code block containing multiple lines
2. Publish the post
3. View the federated content on a remote instance (or inspect the ActivityPub JSON at /wp-json/activitypub/1.0/posts/{id})
4. Verify the code block preserves newlines and formatting

Changelog entry

• [x] Automatically create a changelog entry from the details below.

Changelog Entry Details

Significance

• [x] 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
• [x] Fixed - for any bug fixes
• [ ] Security - in case of vulnerabilities

Message

Preserve whitespace inside preformatted elements when federating content.

[obenland]

Is this ready for review?

[pfefferle]

@obenland Seems to work like expected