swift234

Sema: Disallow potential unavailability on stored properties.

For now, disallow potential unavailability on stored properties. We will
eventually want to support this. Unfortunately, doing so will require changes to
definite initialization and (probably) deinitialization.

We can safely support potential unavailability on lazily initialized
properties (and statics), so suggest a Fix-It that adds a lazy attribute when
the property declaration allows for it.

Swift SVN r27216