[meta.reqmts] UnaryTypeTrait and friends are not in code font in their definition

[timsong-cpp]

After #1151, they are in code font when referred to elsewhere, but not in their definition in [meta.reqmts].

[zygoloid]

*Insertible in [container.requirements.general] use a different convention. *Constructible use a different convention again. We should be consistent across all three, and pick something that's not ugly. But maybe concepts will fix it :)

[AlisdairM]

Many of this concerns were addressed with the introduction of the \oldconcept macro for C++20. Is there any further work outstanding on this ticket?