Login/out: Add a custom login URL setting

[dhruvikpatel18]

What?

Closes #58234

Adds a loginUrl attribute to the Login/out block, so the log in link can point at a custom login page instead of wp-login.php.

Why?

The block currently hardcodes the default WordPress login page via wp_loginout(). Sites that use a membership plugin (or any plugin providing its own front-end login page) have no way to send visitors there from this block, and no way to keep the default login screen out of their navigation. Plugins used to fill this gap, but the issue reports they no longer work, so the option belongs in the block itself.

Testing Instructions

1. Create a page to act as the custom login page (e.g. /sign-in/), or note the URL of one your login plugin provides.
2. In the editor, insert a Login/out block into a template or post.
3. Open the block's Settings panel in the inspector, click the options menu, and enable Custom login URL.
4. Enter the URL from step 1. Leave Redirect to current URL enabled.
5. Save, then view the page as a logged-out visitor (a private window is easiest).
6. Confirm the "Log in" link points at your custom URL with ?redirect_to= set to the current page. Following it should land on your custom login page.
7. Turn Redirect to current URL off and reload, the link should be the bare custom URL, with no redirect_to.
8. Clear the Custom login URL field and reload, the link should return to the default wp-login.php.
9. Log back in and reload, the "Log out" link should be unchanged and still work.
10. With a custom URL set, enable Display login as form. The URL field is hidden, and a logged-out visitor sees the standard login form as before. Disabling the toggle brings the field back with its value intact.

Screenshots or screencast

Screen.Recording.2026-08-20.at.5.02.51.PM.mov

Use of AI Tools

This pull request was authored with help of Claude.

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