[libc][math] Refactor tan implementation to header-only in src/__support/math folder. (#177224)

Part of #147386

in preparation for:

https://discourse.llvm.org/t/rfc-make-clang-builtin-math-functions-constexpr-with-llvm-libc-to-support-c-23-constexpr-math-functions/86450

GitOrigin-RevId: 5234bac082743f070d1aea533f621b9fe0f4d15e