Inconsistent formatting of cv-qualified

[jwakely]

The core and library clauses oscillate between cv-qualified, cv-qualified and (in one case) cv-qualified.

The library is also inconsistent about parenthesising "possibly cv-qualified".

[AlisdairM]

I got some guidance from @zygoloid regarding this on a recent pull request #684 :
"cv should not be italicized except when referencing a metavariable representing a set of cv-qualifiers. That is: "cv-qualified" means "qualified with the set of qualifiers named cv", whereas "cv-qualified" means "qualified with some unspecified cv-qualifiers". See [basic.type.qualifier]/5."