Revert various HNI conversions

Summary: We can't handle a throw through a CoerceStk, so need to revert these for now

Revert "Convert APC to HNI"                                   : de2fb9ff58389c
Revert "Restore some mixed typed arguments with ?string type" : 042433fb53e92b
Revert "Convert string to HNI"                                : f0f3f6d7a938d3
Revert "Get rid of mangle map stuff"                          : 5ea8a1d993fd1f

The mangle map diff is a victim; things wouldn't build unless I reverted that too.

Reviewed By: @bertmaher, @jdelong

Differential Revision: D1601800