appendCodePoint
Appends the Unicode code point represented by codePoint to this StringBuilder.
If codePoint is in the Basic Multilingual Plane (i.e. less than 0x10000), a single character is appended. Otherwise, it is converted to a surrogate pair.
Return
this StringBuilder.
Parameters
codePoint
the Unicode code point to append.
Throws
if codePoint is not a valid Unicode code point.