Feature: #86880 - Enable password view at backend login

See forge#86880

Description

On clicking, the TYPO3 backend login now displays an additional button to reveal the user's password, once something has been typed in the password field.

Impact

A user who is about to log in to the backend is now able to reveal the typed password. Once the password field is cleared, the visibility mode automatically switches back to its default to avoid revealing sensitive data by accident.