Table: support initializer list constructor. (#915)

To avoid burdening the user with explicit type construction when using
the library, we can use a constructor that accepts an initializer list
(std::initializer_list). This allows users to pass initializer lists
directly without having to wrap them in
std::vector<std::vector<std::string>>. This resolves the ambiguous case
when the inner list contains only two elements.

Bug:https://github.com/ArthurSonzogni/FTXUI/issues/912