Add dynamic enforcement of exclusive access when a KeyPath directly accesses a final
stored property on an instance of a class. For read-only projections, this begins and ends
the access immediately. For mutable projections, this uses the ClassHolder to perform
a long-term access that lasts as long as the lifetime of the ClassHolder.
rdar://problem/31972680
This converts the instances of the pattern for which we have a proper
substitution in lit. This will make it easier to replace it
appropriately with Windows equivalents.
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)
