Debug transformer that records the stack which triggered the load of one or more watched classes.
Writing each captured stack to
logs/mixinbooter.log. This helps diagnose
"mixin target was loaded too early" issues. As once a class is defined, its mixins can no longer apply,
and by the time the mixin subsystem notices, the causal stack is gone.
Watched class names are supplied through the mixinbooter.watchedClasses system property
(comma-separated), populated from the debug.watchedClasses option in config/mixinbooter.cfg.
The single token * enables "watch all" mode, tracing the load of every class (very verbose, each class
traced once). The transformer is inert (a single property read per class) until the property is set.