Turn many optimized-out value functions into methods

This turns many functions that are related to optimized-out or
availability-checking to be methods of value.  The static function
value_entirely_covered_by_range_vector is also converted to be a
private method.

Approved-By: Simon Marchi <simon.marchi@efficios.com>

gdb/python/py-value.c

@@ -1197,7 +1197,7 @@ valpy_get_is_optimized_out (PyObject *self, void *closure)
 
   try
     {
-      opt = value_optimized_out (value);
+      opt = value->optimized_out ();
     }
   catch (const gdb_exception &except)
     {