The three options are now:
* `explicit`: Enforce Sendable constraints where it has been explicitly adopted and perform actor-isolation checking wherever code has adopted concurrency. (This is the default)
* `targeted`: Enforce Sendable constraints and perform actor-isolation checking wherever code has adopted concurrency, including code that has explicitly adopted Sendable.
* `complete`: Enforce Sendable constraints and actor-isolation checking throughout the entire module.
This patch delays the removal of redundant isolation for inferred
global-actor isolation to Swift 6 too, since we only warn about it
changing in Swift 5. Otherwise, only isolation that is a byproduct
of inference no longer needs an await, which will probably confuse
people.
This change is with respect to SE-327, which argues that the
non-static stored properties of ordinary structs do not need
global-actor isolation.
If a struct is a property-wrapper, then global-actor isolation
still applies to the `wrappedValue`, even if it's a stored property.
This is needed in order to support the propagation of global-actor
isolation through the wrapper, even when the programmer has opted
to use a stored property instead of a computed one for the
`wrappedValue`. Since this propagation is a useful pattern, I think
this exception is reasonable.
