Allow regular expressions used in user restrictions to match homographic characters

I have not yet created an issue fork for this issue because, the more I think about it, the more I think that any change done in #85826: Prevent homographic usernames would fix this issue too. That is because usernames that are not allowed by Drupal core cannot be made possible by the User Restrictions module, except in the case this module removes all the constraints added by Drupal core, which is not what this module should do.

This is really true also for not homographic characters: Drupal core does not allow a username that starts with a space, ends with a space, nor a username that contains two spaces in row. This module cannot allow those usernames, but the module does not give a warning for regular expressions that allow a space at the beginning of a username.
This means that the module should not give any warning for regular expressions that allow homographic characters. It should either apply the regular expressions entered by people without making any change to the regular expressions nor to the value used by those regular expressions to check the entered username or use the transliterated username as value the regular expressions need to check.

I changed the title because, more than preventing usernames which contains homographic characters, which is a task for Drupal core, this module should allow the regular expressions to match also homographic characters.

Furthermore, allowing a regular expression to match homographic characters should be done for usernames, but also for other fields which allow entering Unicode characters.