Remove all uses of the `TYPE_FIELDS` macro. Replace them with either:
1) type::fields, to obtain a pointer to the fields array (same as
TYPE_FIELDS yields)
2) type::field, a new convenience method that obtains a reference to one
of the type's field by index. It is meant to replace
TYPE_FIELDS (type)[idx]
with
type->field (idx)
gdb/ChangeLog:
* gdbtypes.h (struct type) <field>: New method.
(TYPE_FIELDS): Remove, replace all uses with either type::fields
or type::field.