to_utf8:
U+0001 = [1]
U+007f = [127]
U+07ff = [223, 191]
U+263f = [226, 152, 191]
U+ffff = [239, 191, 191]
U+10000 = [240, 144, 128, 128]
U+10ffff = [244, 143, 191, 191]
U+d800 invalid
U+dbff invalid
U+dc00 invalid
U+dfff invalid

to_utf16:
U+0001 = [1]
U+007f = [127]
U+07ff = [2047]
U+263f = [9791]
U+ffff = [65535]
U+10000 = [55296, 56320]
U+10ffff = [56319, 57343]
U+d800 invalid
U+dbff invalid
U+dc00 invalid
U+dfff invalid

is_surrogate: okay

is_noncharacter: okay