Add nqp::captureexistsnamed.

Author: jnthn

src/QAST/Operations.nqp

@@ -1061,6 +1061,7 @@ QAST::Operations.add_core_pirop_mapping('captureposarg', 'set', 'PQi');
 QAST::Operations.add_core_pirop_mapping('captureposarg_i', 'set', 'IQi');
 QAST::Operations.add_core_pirop_mapping('captureposarg_n', 'set', 'NQi');
 QAST::Operations.add_core_pirop_mapping('captureposarg_s', 'set', 'SQi');
+QAST::Operations.add_core_pirop_mapping('captureexistsnamed', 'exists', 'IQs');
 QAST::Operations.add_core_pirop_mapping('captureposprimspec', 'captureposprimspec', 'IPi');
 
 # Multiple dispatch related.