This renames the backend packages to more closely align with the
new direction for them. Namely, pkg/backend/cloud becomes
pkg/backend/httpstate and pkg/backend/local becomes
pkg/backend/filestate. This also helps to clarify that these are meant
to be around state management and so the upcoming refactoring required
to split out (e.g.) the display logic (amongst other things) will make
more sense, and we'll need better package names for those too.
These changes enable tracing of Pulumi API calls.
The span with which to associate an API call is passed via a
`context.Context` parameter. This required plumbing a
`context.Context` parameter through a rather large number of APIs,
especially in the backend.
In general, all API calls are associated with a new root span that
exists for essentially the entire lifetime of an invocation of the
Pulumi CLI. There were a few places where the plumbing got a bit hairier
than I was willing to address with these changes; I've used
`context.Background()` in these instances. API calls that receive this
context will create new root spans, but will still be traced.
* Refactor the SnapshotManager interface
Lift snapshot management out of the engine by delegating it to the
SnapshotManager implementation in pkg/backend.
* Add a event interface for plugin loads and use that interface to record plugins in the snapshot
* Remove dead code
* Add comments to Events
* Add a number of tests for SnapshotManager
* CR feedback: use a successful bit on 'End' instead of having a separate 'Abort' API
* CR feedback
* CR feedback: register plugins one-at-a-time instead of the entire state at once
* Re-introduce interface for snapshot management
Snapshot management was done through the Update interface; this commit
splits it into a separate interface
* Put the SnapshotManager instance onto the engine context
* Remove SnapshotManager from planContext and updateActions now that it can be accessed by engine Context
