Add honeypot fields and minimum fill-out time for sign-up form (#15276)

* Add honeypot fields to limit non-specialized spam

Add two honeypot fields: a fake website input and a fake password confirmation
one. The label/placeholder/aria-label tells not to fill them, and they are
hidden in CSS, so legitimate users should not fall into these.

This should cut down on some non-Mastodon-specific spambots.

* Require a 3 seconds delay before submitting the registration form

* Fix tests

* Move registration form time check to model validation

* Give people a chance to clear the honeypot fields

* Refactor honeypot translation strings

Co-authored-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/styles/mastodon/forms.scss

@@ -354,6 +354,7 @@ code {
   input[type=number],
   input[type=email],
   input[type=password],
+  input[type=url],
   textarea {
     box-sizing: border-box;
     font-size: 16px;
@@ -994,3 +995,10 @@ code {
     flex-direction: row;
   }
 }
+
+.input.user_confirm_password,
+.input.user_website {
+  &:not(.field_with_errors) {
+    display: none;
+  }
+}