getDriveLetter

fn getDriveLetter(comptime T: type, path: []const T) []const T {
    const len: usize = switch (T) {
        // getWin32PathType will only return .drive_absolute/.drive_relative when there is
        // (1) a valid code point, and (2) a code point < U+10000, so we only need to
        // get the length determined by the first byte.
        u8 => std.unicode.utf8ByteSequenceLength(path[0]) catch unreachable,
        u16 => 1,
        else => @compileError("unsupported type: " ++ @typeName(T)),
    };
    return path[0..len];
}