Determines whether a UTF-16 character is defined as a high surrogate in the Unicode specifications.

class function IsHighSurrogate(C: Char): Boolean; overload;
class function IsHighSurrogate(const S: string; Index: Integer): Boolean; overload;

__fastcall Boolean IsHighSurrogate(Char C);
__fastcall Boolean IsHighSurrogate(const AnsiString S, int Index);