Add explicit character encoding specifications in 39 more RGL modules

To silence warnings and avoid potential problems after changing the default
encoding to UTF-8.

lib/src/arabic/AdverbAra.gf

@@ -1,4 +1,5 @@
 concrete AdverbAra of Adverb = CatAra ** open ResAra, Prelude in {
+  flags coding=utf8;
 
   lin
     PositAdvAdj a = {s = a.s ! APosit Masc Sg Indef Acc} ;

lib/src/arabic/IdiomAra.gf

@@ -1,4 +1,5 @@
 concrete IdiomAra of Idiom = CatAra ** open Prelude, ResAra in {
+  flags coding=utf8;
 --
 --  flags optimize=all_subs ;
 --

lib/src/arabic/PhraseAra.gf

@@ -2,6 +2,7 @@ concrete PhraseAra of Phrase = CatAra ** open
   ParamX, 
   Prelude, 
   ResAra in {
+  flags coding=utf8;
 
   lin
     PhrUtt pconj utt voc = {s = pconj.s ++ utt.s ! Masc ++ voc.s} ;--FIXME

lib/src/arabic/RelativeAra.gf

@@ -1,4 +1,5 @@
 concrete RelativeAra of Relative = CatAra ** open ResAra in {
+  flags coding=utf8;
 --
 --  flags optimize=all_subs ;
 --