Instead of snprintf.
Because some standalone code uses those functions directly or indirectly,
and PrintfTarget lives in mozglue, they now need to depend on mozglue
instead of mfbt. Except logalloc/replay, which cherry-picks what it
uses, and the updater, for which we keep using vsnprintf.
Differential Revision: https://phabricator.services.mozilla.com/D103730