[fpc-pascal] UnicodeString and surrogate pairs

[Marco van de Voort]

In our previous episode, Graeme Geldenhuys said:
> Does FPC's RTL (or FCL) include a function to check for UTF-16 surrogate
> pairs? I'd be very surprised if there isn't, but I have yet to find it
> in the documentation or source code I searched.

Same as Delphi, character.tcharacter.issurrogate() or
character.issurrogate()

(modern delphi units group everything as class methods in classes for some vague
reason)