A superclass requirement 'T : C' implies a layout requirement
'T : AnyObject' (if the class is @objc) or 'T : _NativeObject'
(if the class is not @objc).
In the latter case, there might already be a 'T : AnyObject'
requirement, in which case the type parameter 'T' is subject
to two layout requirements:
T : AnyObject
T : _NativeObject
The second requirement implies the first however. To encode this
in the world of rewrite loops, we the notion of a 'relation'
between property symbols, and a 'Relation' rewrite step.
Here, the relation is that _NativeObject < AnyObject. Once this
relation is recorded, the Relation rewrite step will transform
T.[layout: _NativeObject].[layout: AnyObject]
into
T.[layout: _NativeObject]
and vice versa.
This rewrite step allows us to construct a rewrite loop which
makes the first rewrite rule redundant via the second.
Using the qualified name is subtly different from scoping the function.
Use the latter, which correctly places the function into the namespace,
to enable building with VS2022.
When a rewrite rule is replaced with a path containing ::Adjust, ::Decompose,
::ConcreteConformance or ::SuperclassConformance rewrite steps, the steps
will get a non-zero EndOffset if the original rule appears in a step with a
non-zero EndOffset.
For this reason, these steps must work with a non-zero EndOffset, which
primarily means computing correct offsets into the term being manipulated.
For homotopy reduction to properly deal with new rules introduced
while bulding the property map, rewrite loops must be recorded
relating these to existing rules.
For homotopy reduction to properly deal with rewrite rules
introduced by property map construction, we need to keep
track of the original property rules when recording properties
in property bags.
For now, this doesn't even attempt to handle unification or
conflicts; we only record the first rule for each kind of
property on a fixed key.
This isn't actually used for anything yet, except a new
verify pass that runs after property map construction.
