swift234

introduce a new "IsDirectIVarAccess" bit to MemberRefExpr.  Properties
that have both storage AND accessors are accessed by-default through
their accessors.  This bit indicates that a specific MRE should access
the storage instead.

Use this new bit in the synthesized getter/setter for "StorageObjC"
properties (it will also be used for other things in the future).
This also teaches SILGen about it.

One interesting aspect of this representation is that it makes it trivial
to add some expression syntax for directly accessing a store+computed 
property (e.g. ObjC properties, also someday didSet/willSet properties) 
someday if we care.  This would be analogous to the "self->ivar" syntax
in objc (vs self.ivar).  No, we will not use "->" for this. :-)

NFC since this is the use is still hidden under the -enable-new-objc-properties
staging option.



Swift SVN r12965