Raise with LWG: Does hardcoded `size_t` pose problems for containers with extended integral sizes?

[Zach Laine]

[flatmap.capacity] p2

Can size_type == size_t be smaller than one of the container size_types,
e.g. when the latter are extended integer types?

I don't know.  This is like this because Marshall suggested to
hard-code size_t from the beginning, and no one has objected since.

Seems important to find out.  I want to know what happens if the min
"overflows" and thus loses information.  I think we cater for
extended integer types elsewhere, too.