swift234

Representational changes towards get-and-mutableAddress
properties.

The main design change here is that, rather than having
purportedly orthogonal storage kinds and has-addressor
bits, I've merged them into an exhaustive enum of the
possibilities.  I've also split the observing storage kind
into stored-observing and inherited-observing cases, which
is possible to do in the parser because the latter are
always marked 'override' and the former aren't.  This
should lead to much better consideration for inheriting
observers, which were otherwise very easy to forget about.
It also gives us much better recovery when override checking
fails before we can identify the overridden declaration;
previously, we would end up spuriously considering the
override to be a stored property despite the user's
clearly expressed intent.

Swift SVN r22381