Fix passing non null terminated strings for null terminated params

[smilediver]

Fixes some cases where std::string_view is passed to [NSString stringWithUTF8String:]. stringWithUTF8String expects a zero terminated string.

[halx99]

caller should ensure string_view is null-terminated

[smilediver]

caller should ensure string_view is null-terminated

No, that's a bad idea. The whole purpose of std::string_view is to represent a non null-terminated string. So if API takes std::string_view, then it must treat it as not null-terminated.