(Ara) Add a distinction in CN and NP whether it's heavy

This makes a difference in word order; default is VSO, but if the
subject NP is complex, e.g. coming from RelNP or SentCN,
the more natural word order is SVO.

Example that triggered the change comes from an application grammar:

Gold standard by informant: مَا تَوَصْلّنَا إلَيهِ يَبْدُو مَنْطِقِيَّاً
Grammar before change: يَشْعُرُ مَاً نَتَوَصَّلُ إِلَىهُ مَنْطِقِيّاً
Grammar after change:  مَاً نَتَوَصَّلُ إِلَىهُ يَشْعُرُ مَنْطِقِيّاً

src/arabic/ConjunctionAra.gf

@@ -5,7 +5,7 @@ lincat
 
   [S] =  {s1,s2 : Order => Str} ;
   [Adv] = {s1,s2 : Str} ;
-  [NP] = {s1,s2 : Case => Str ; a : Agr ; empty : Str} ;
+  [NP] = {s1,s2 : Case => Str ; a : Agr ; empty : Str; isHeavy : Bool} ;
   [AP] = {s1,s2 : Species => Gender => Number => State => Case => Str} ;
 
 lin
@@ -21,16 +21,19 @@ lin
 
   BaseNP x y = twoTable Case x y ** {
     a = conjAgr x.a y.a ;
-    empty = []
+    empty = [] ;
+    isHeavy = True ;
     } ;
   ConsNP xs x = consrTable Case comma xs x ** {
     a = conjAgr xs.a x.a ;
-    empty = []
+    empty = [] ;
+    isHeavy = True ;
     } ;
   ConjNP conj ss = conjunctDistrTable Case conj ss ** {
     a = let gn = pgn2gn ss.a.pgn in
         {pgn = Per3 gn.g (conjNumber conj.n gn.n) ; isPron = False} ;
-    empty = []
+    empty = [] ;
+    isHeavy = True ;
     } ;
 
   BaseAP = twoTable5 Species Gender Number State Case ;