Add password autocomplete hints (#20071)

Fixes #20067

Our password autocomplete hints were “off” but that does not prevent current
browsers from trying to autocomplete them anyway, so use `current-password` and
`new-password` so they don't put a newly-generated password in a password
confirmation prompt, or the old password for a password renewal prompt.

app/views/auth/sessions/new.html.haml

@@ -12,7 +12,7 @@
       - else
         = f.input :email, autofocus: true, wrapper: :with_label, label: t('simple_form.labels.defaults.email'), input_html: { 'aria-label' => t('simple_form.labels.defaults.email') }, hint: false
     .fields-group
-      = f.input :password, wrapper: :with_label, label: t('simple_form.labels.defaults.password'), input_html: { 'aria-label' => t('simple_form.labels.defaults.password'), :autocomplete => 'off' }, hint: false
+      = f.input :password, wrapper: :with_label, label: t('simple_form.labels.defaults.password'), input_html: { 'aria-label' => t('simple_form.labels.defaults.password'), :autocomplete => 'current-password' }, hint: false
 
     .actions
       = f.button :button, t('auth.login'), type: :submit