Take Version and PicsarVersion out of the WarpX class

[lucafedeli88]

This PR takes Version and PicsarVersion out of the WarpX class and puts them in a warpx namespace.
The goal is twofold: 1) reducing the complexity of the WarpX class 2) possibly avoid in the future the inclusion of the huge WarpX class where we only need the version of WarpX and Picsar.

With the occasion, the two functions are made noexcept and [[nodiscard]].

[ax3l]

ok :)

[ax3l]

Restarting CI

[ax3l]

Restarting CI

[ax3l]

@lucafedeli88 I think the GNU makefile needs a touch-up for this to pass.

[lucafedeli88]

@lucafedeli88 I think the GNU makefile needs a touch-up for this to pass.

@ax3l , I had a look at the GNU makefile. It seems to me that when we compile with the GNU makefile there is an AMReX tool that takes care of generating Utils/WarpXVersion.H.in .

The solution I chose is to leave Utils/WarpXVersion.H.in untouched and implement warpx::Version and warpx::PicsarVersion inside Utils/WarpXGetVersion.H/cpp. It seems to work on my computer.