Fix preserve URL fragments on multi-tabs sign-ins

What does this MR do and why?

Fix preserve URL fragments on multi-tabs sign-ins

When multiple sign-in methods are enabled, a multi-tab selection is rendered on the sign-in pages. When there is a URL fragment, the actions' URL in each of the forms should append the URL fragment, except in the form rendered by the SignInForm Vue component, which has this ID: <form id='sign-in-form'>.

On the second commit, we remove the unit tests and replace them for integration tests. The nature of this JS functionality is better tested in the context of integration tests.

Changelog: fixed

References

Noticed here: !220252 (comment 3051556021)

Bug introduced here: !209857 (merged)

Issue: #590497 (closed)

Screenshots or screen recordings

No changes

How to set up and validate locally

1. Enable LDAP, Crowd or Smartcard
2. Go to https://gdk.test:3443/users/sign_in#59
3. Make sure that the #59 fragment is in the action attribute of the forms.

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