Add recursion protection when emitting deprecation warnings for class
constants, since the deprecation message can come from an attribute that is
using the same constant for the message, or otherwise result in recursion.
But, internal constants are persisted, and thus cannot have recursion
protection. Otherwise, if a user error handler triggers bailout before the
recursion flag is removed then a subsequent request (e.g. with `--repeat 2`)
would start with that flag already applied. Internal constants can presumably
be trusted not to use deprecation messages that come from recursive attributes.
Fixes GH-18463
Fixes GH-17711
cd751f98cb