[cppia] Generate full debug source paths (#12053)

* [cppia] Allow generating full debug source paths

* Use full debug paths in cppia in all cases

Without these paths being absolute, cppia break points cannot work at
all, so it makes more sense for this to just be the default. These paths
are only ever added for debugging anyway.

src/generators/cpp/gen/cppCppia.ml

@@ -786,7 +786,7 @@ class script_writer ctx filename asciiOut =
     method wpos p =
       if debug then
         this#write
-          (this#fileText p.pfile ^ "\t"
+          (this#fileText (Path.get_full_path p.pfile) ^ "\t"
           ^ string_of_int (Lexer.get_error_line p)
           ^ indent)