In AccessEnforcementSelection, treat passing a projection from a box to
a partial_apply as an escape to force using dynamic enforcement on the box.
This will now correctly use dynamic enforcement on variables that are taken
as inout and also captured by storage address in a closure:
var x = ...
x.mutatingMethod { ... use x ...}
but does pessimize some of our existing enforcement into dynamic since
access enforcement selection.
Ideally we would distinguish between escaping via an nonescaping closures
(which can only conflict with accesses that are in progress) and
escaping via escaping closures (which can conflict for any reachable code
after the escape)
