Type checking associated constants can require trait bounds, but an empty
parameter environment was provided to the trait solver.  Providing an
appropriate parameter environment seems to fix #54822 and also make one of the
cases in src/test/ui/nll/trait-associated-constant.rs that should compile
successfully do so.  It also (slightly) improves the error message in
src/test/ui/associated-const/associated-const-generic-obligations.rs