Login screen's Register link drops the redirect_to it was given

[arunshenoy99]

Sending someone to login.wordpress.org with a redirect_to works if they log in. If they click Register on that screen instead, the redirect_to is dropped: that link is a bare ​https://login.wordpress.org/register.

Steps to reproduce:

1. Open ​https://login.wordpress.org/?redirect_to=https%3A%2F%2Fwordpress.org%2Fsupport%2F
2. The login form's hidden redirect_to field holds ​https://wordpress.org/support/, so logging in returns the person there.
3. Click Register. The only register link on the page is ​https://login.wordpress.org/register, with no redirect_to, so after signing up there is nowhere to send them back to.

/register does honour a redirect_to when it is given one: request it as ​https://login.wordpress.org/register?redirect_to=... and the hidden field renders. The register links in the global header and the profiles nav already pass one, as in #6296. So the login screen's link looks like it just needs to forward what it was handed.

Where this costs something today is WordCamp ticket sales. CampTix sends a logged-out buyer to:

https://login.wordpress.org/?from=bengaluru.wordcamp.org
  &redirect_to=<tickets URL carrying the ticket selection>
  &locale=en_US&wcname=WordCamp+Bengaluru+2026

A buyer who logs in comes back with their tickets still selected. A buyer who creates an account comes back to an empty ticket form showing a total of 0, and has to work out for themselves that they need to pick again.

Related: ​https://github.com/WordPress/wordcamp.org/issues/2014