devel/stc: [NEW PORT] Modern, user-friendly, generic, type-safe and fast C99 library

STC is a mature, comprehensive, general purpose container and
algorithm library for C99/C11. It has excellent ergonomics and
requires virtually no boilerplate code. The library adds many missing
features to C, like common data containers, algorithms, and
abstractions found in contemporary system languages like Zig, Rust,
and C++. Containers and algorithms are templated or generic, which
allows for a fully typesafe, compact, and high performance
implementation.

WWW: https://github.com/stclib/STC/

Approved by: yuri@ (Mentor)

Differential Revision: https://reviews.freebsd.org/D52520