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-prettyprint.c

@@ -582,7 +582,7 @@ gdbpy_apply_val_pretty_printer (const struct extension_language_defn *extlang,
     value->fetch_lazy ();
 
   /* No pretty-printer support for unavailable values.  */
-  if (!value_bytes_available (value, 0, type->length ()))
+  if (!value->bytes_available (0, type->length ()))
     return EXT_LANG_RC_NOP;
 
   if (!gdb_python_initialized)

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)
     {