Freestanding meta

A very basic port of GCC16's <meta> to a freestanding environment.

If __STDC_HOSTED__ is not true, it implements comptime versions of std::vector, std::string, std::optional, and std::string_view. Otherwise it includes the appropriate system headers for those.

Replacing std::vector with any other namespace/typename breaks it, it does work for the others, but std::vector seems to be an internal compiler issue, so I kept the std:: prefix for all others, for the sake of consistency. I tried using freestanding_meta:: prefixes for each type, except this broke std::vector, and only std::vector.

Changes made to fs_meta.h:

• added at line 643 __detail::__statically_sized as a replacement for ranges::__static_sized_range since that was not found.
• changed includes <optional>, <string>, <string_view>, and <vector> to "fs_*," alternatives.

LICENSE

LICENSE covers every file except fs_meta.h
LICENSE.GCC covers fs_meta.h