_gtkTextWrapSet sets whether to wrap lines never, at word boundaries,
or at character boundaries to a Text object.
Other functions allow to set this to some parts of a text.
Prototype : fun [ObjGtkText I] ObjGtkText
ObjGtkText : a Text object.
I : a wrap mode :
WRAP_NONE : do not wrap lines (default)
WRAP_CHAR : wrap text, breaking lines anywhere the cursor can appear
WRAP_WORD : wrap text, breaking lines in between words
WRAP_WORD_CHAR : wrap text, breaking lines in between words, or if that is not enough, also between graphemes.
Return ObjGtkText : the same Text object
or nil if an error occurs.