[Accepted with revision] SE-0395: Observability

[dmt (Dima Galimzianov)]

@tcldr

This would allow dependent observers to make any changes they need to make within SwiftUI's deadline for the current event loop.

It doesn't need to be anything huge for this version of the proposal, something as simple as changing withObservationTracking(_:onChange:) to withObservationTracking(_:willChange:didChange:) could lay the foundation.

This is what I tried to raise in the review as well, but unfortunately it wasn't discussed.
The thing is observing didSets is not enough. willSet has the invariant "subscribers will receive a notification before anything is changed", but didSet doesn't have the invariant "subscribers will receive a notification after everything is changed". To support this invariant we need transactions.