Updated FTXUI version from 4.0.0 to 5.0.0

[lesserfish]

Currently, CMake fetches FTXUI's content from the 4.0.0 version of FTXUI.

Because of this, some of the examples provided in the main github repository of FTXUI won't work. (For example: examples/component/window.cpp will not work).

I've updated the GIT_TAG version from "v4.0.0" to "v5.0.0" to ensure that all examples work.

[dacharyc]

+1. I was coming here to make the same PR - bumping the version got me going with this example. It would be great if this could get merged.

[ArthurSonzogni]

Thanks you! Sorry for the late approval.

[ArthurSonzogni]

(It can be closed, because another PR did something similar)