Vaadin 24.9+ ``VaadinWebSecurity`` deprecated

[AB-xdev]

VaadinWebSecurity was deprecated in 24.9.
According to the docs one should use VaadinSecurityConfigurer instead.

Problem: VaadinSecurityConfigurer is final so you can't extend it and it also has a private constructor so you can't instantiate it -.-

Upstream: vaadin/flow#22293

Probable solution: "rebase" our code onto VaadinSecurityConfigurer or - if they refuse to make it accessible - copy the code / use the reflection crowbar.

[AB-xdev]

Solved the problem by wrapping Vaadin's solution.
Might be kind of ugly but it works for now...