GenEx: add PREDICATE selector to $<LIST:TRANSFORM> Add a PREDICATE selector to $<LIST:TRANSFORM> that chooses which elements to transform by evaluating a <body> per element (with $<_0> bound) and acting on those for which it yields "1". This selects by computed condition instead of the fixed AT/FOR/REGEX positions, so any generator expression -- including target queries -- can decide where an action applies. It works with both the canned actions and APPLY. Issue: #27892