Fix likes and reposts showing in standard Comments block when other plugins also filter comment types

[pfefferle]

Fixes #2747

Proposed changes:

When another plugin (e.g. Friends, Webmention, Event Bridge) registers a pre_get_comments callback that sets type__not_in, ActivityPub was silently skipping its own exclusion of likes, reposts, and quote comment types. This caused those interactions to appear in the standard WordPress Comments block even when the Fediverse Reactions block was also present on the page.

The fix merges ActivityPub's comment type exclusions with any existing type__not_in values instead of bailing out early when type__not_in is already set.

Other information:

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

Testing instructions:

1. Install a plugin that adds custom comment types to type__not_in via pre_get_comments (e.g. Webmention, Friends).
2. Receive a Like or Repost on a post from the Fediverse.
3. View that post on the front end with both the standard Comments block and the Fediverse Reactions block present.
4. Before fix: Likes/Reposts appear in the standard Comments block.
5. After fix: Likes/Reposts are correctly excluded from the standard Comments block and only appear in the Fediverse Reactions block.

Changelog entry

Significance: Patch, Type: Fixed

Fix likes and reposts appearing in the standard Comments block when another plugin also filters comment types.