Reject every interface member that uses a reserved name, static members included

Start with protocol_interface_function_infos, named_member_function_infos, and the StaticInterfaceMemberWithReservedNameIsIgnored test to understand the current filtering. Review DRAFT.md's “Reserved member names” section and the rejected/ignored lists in #407, then confirm the intended rule with the issue options. Done means the selected behavior is covered by tests and the related documentation and reserved-name lists are consistent.

Follow-up to #318, from the review of #449: https://github.com/jbcoe/cc-protocol/pull/449#discussion_r4057463300

#449 rejects a non-static interface member function named allocator_type, get_allocator or swap. A static member function with one of those names is skipped before the check, like every other static:

struct I {
  static void swap(I&, I&) noexcept;  // accepted and ignored
};

Nothing is hidden today, because interface statics are not forwarded. The case for rejecting it anyway:

• The rule is simpler to state: an interface cannot declare a member with a reserved name.
• Removing static later turns an accepted interface into a rejected one.
• If interface statics are ever forwarded, the reserved name would hide the generated member silently, which is what #318 set out to stop.

The same argument covers members the check never sees. named_member_function_infos filters on is_function, so a data member, static data member, alias or nested type with a reserved name is accepted too:

struct I {
  using allocator_type = int;  // accepted and ignored
  int swap;                    // accepted and ignored
};

Options:

1. Reject a static member function with a reserved name. Move has_reserved_member_name above the is_static_member skip in protocol_interface_function_infos.
2. Reject any member with a reserved name, whatever its kind. Walk members_of the interface once, before the function filter.
3. Leave statics and non-function members ignored, and say so in DRAFT.md.

2 gives the rule DRAFT.md can state in one sentence. Other statics stay ignored either way (#211, #403).

To change with it: the StaticInterfaceMemberWithReservedNameIsIgnored test, the "non-static member function" wording in DRAFT.md's "Reserved member names", and the rejected/ignored lists in #407. #450 adds protocol and protocol_view to reserved_member_names; the same rule should apply to them.