Add Merge() specializations to support more Element containers

[nbusser]

Related issue

#1108

Description

Merge() was previously only supporting Elements as a Element container.
This PR adds specialization for:

• all the containers that matches the concept std::ranges::range
• std::queue
• std::stack

Interrogation

I did not find a clear reference about the C++ standard that FTXUI claims to support.

@ArthurSonzogni Is it ok to use C++20 concepts here, or should FTXUI be compatible with older C++ standards? In that case I will change the PR content accordingly.

[ArthurSonzogni]

@ArthurSonzogni Is it ok to use C++20 concepts here, or should FTXUI be compatible with older C++ standards? In that case I will change the PR content accordingly.

Yes, I am not going to drop C++17 users soon. Could you please wrap the C++20 parts behind:

#if __cplusplus >= 202002L
...
#endif