https://bugzilla.mozilla.org/show_bug.cgi?id=957358
957358 - Restrict everything in Char16.h to C++
RESOLVED (ehsan.akhgari) in Core - XPCOM. Last updated 2020-12-09.
restricteverything
https://timsong-cpp.github.io/cppwp/n4861/char.traits.specializations.char16.t
[char.traits.specializations.char16.t]
chartraitsspecializations