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/RelativeAra.gf

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