Tweak members_of note that not only special members may be implicitly…

[jakubjelinek]

…-declared.

[jakubjelinek]

@jwakely @tomaszkam

In e.g.

struct S { auto operator <=> (const S &) const = default; int s; };

bool operator == (const S &) const = default; is implicitly-declared and std::members_of should first list the explicitly declared members, operator <=> and s and only after that the implicitly-declared ones, 6 special members and operator ==.

[jakubjelinek]

Implicitly-declared needs to apply both to special members and comparison operator member functions, not sure if it doesn't have to be repeated.

[tomaszkam]

Looks good to me.

[jwakely]

Please adjust the commit message so the first line starts with the stable tag, e.g.

[meta.reflection.member.queries] tweak members_of note about implicitly-declared members