Produces more helpful (and harder-to-miss) error messages when a hook
emits an error. Also advises run-hook when doom-debug-mode is active, so
errors in hooks (generally, major mode hooks) don't quietly go
unnoticed.
More in line with Emacs' built-in practice of storing a variable's
standard-value in a symbol property of the same name, with the added
benefit of less global state.
