JS and XML files have to be UTF-8 encoded.
Internaly we often use wchar_t to address "all" characters. This uses more memory and is not always usable: std::ifstream https://code.wildfiregames.com/D4741
When char would be UTF-8 encoded we could address all unicode-characters while using char-api.
We should not wait for C++20 char8_t since there is even less char8_t-api.
This patch staticly asserts if char is UTF-8 encoded.
Is this the right way/place to ensure this? Should it be in the build system?