Support char8_t arrays/containers as inputs for deserialization

[fktn-k]

Since C++20 and later, the string literal u8"" returns a char8_t[N] object, instead of a char[N] object, which has broken backward compatiblity with the code compiled with C++17 or earlier.
The issue above has an impact on the fkYAML library whose deserialization feature can accept the return value of the u8"" literal.
So, in this topic, fkYAML supports char8_t literals as inputs for deserialization when compiled with C++20 or later.

[fktn-k]

Being addressed in the branch feature/237_support_char8_t_in_deserialization.

[fktn-k]

Completed with PR #269.