Fix remainder of #9681 (textcyrillic and textgreek handling).

Fix remainder of #9681 (textcyrillic and textgreek handling).

* Fix macro termination if \textcyrillic or \textgreek is not required
  for Greek or Cyrillic letter.

* Replace "writeScriptChars" with conditionals in the character-output loop in
  "Paragraph::latex" (solves "FIXME: modifying i here is not very nice...").

The font changing commands \textcyrillic and \textgreek are no longer
part of the textcommand in "lib/unicodesymbols" but added when required
in Paragraph::Private::latexSpecialChar.