This branch uses EventKit, an ultra-simple library for implementing
events. The object implementing the methods maintains its own emitter
object rather than doing a mixin like Emissary encourages. This will
make it easier for us to deprecate ::on on the object itself. Unlike
emissary, the EventKit Emitter implements a super minimalistic API that
only allows one value to be emitted and always returns a Disposable
from subscriptions.
Fixes#2694
Fixel #2853
Previously, we were storing an `active` boolean for each pane. We've
had some strange bugs where every pane is serializing `active: false`,
which causes exceptions when loading up the stored data.
This new approach serializes the activePaneId on the PaneContainer
itself. Since the PaneContainer is the source of truth regarding the
active pane, it makes more sense to handle it here.
This unfortunately changes the serialization version for the
PaneContainer, so people won't have their state persisted after
upgrading. But it seems better than leaving cruft to handle the old
serialization situation.
This causes the active item to change in the model before the associated
view can be added, which causes problems with the ReactEditorView having
methods called on it before its afterAttach hook creates the component.
We call Pane::activate subsequently unless activation is suppressed,
which will focus the pane anyway, so this was redundant.
We always want to preserve at least one pane, so we don't call destroy
on the pane if it is the last pane. However, we still want to destroy
its items. This was previously relying on the view to destroy the
underlying item, which isn't as reliable as doing it in the model.
This was previously throwing an error when Workspace::open was called
with a split: right option and the rightmost sibling was a PaneAxis
since it was assuming findOrCreateRightmostSibling was always returning
a Pane, not a PaneAxis.
