Custom rewrite endpoints and wp_old_slug_redirect

[batmoo]

Previously: #33920

wp_old_slug_redirect currently only handles core rewrite endpoints (like feed and embed). If you have a custom rewrite endpoint, you end up redirected back to the new permalink.

You can use the [old_slug_redirect_url ​https://developer.wordpress.org/reference/hooks/old_slug_redirect_url/] filter to redirect correctly but the filter does not pass the post id, which makes things a bit challenging (especially if you need to do any processing beyond just appending the endpoint).

It would be nice if the post id was passed into the old_slug_redirect_url filter:

$link = apply_filters( 'old_slug_redirect_url', $link, $id );

It would be even nicer if the redirect handled custom endpoints automatically as well.

[MikeSchinkel]

Patch to include $id as a parameter

## Summary

This updates wp_old_slug_redirect() to pass the resolved redirect post ID to the old_slug_redirect_url filter.

## Why

Callbacks filtering the old slug redirect URL currently receive only the generated redirect URL. Passing the post ID gives callbacks enough context to inspect the matched post before changing or disabling the redirect.

## Use of AI Tools

AI assistance: Yes
Tool(s): ChatGPT, Codex
Model(s): GPT-5.5
Used for: Initial code review, and test suggestions; final implementation and tests were reviewed and edited by me.

## Testing

Ran:

npm run test:php -- --filter Tests_Rewrite_OldSlugRedirect

## Trac Ticket

https://core.trac.wordpress.org/ticket/39442