Modal dialogs can be presented while other modal dialogs are already
being displayed. Previously, dialogs were always displayed in the order
they were requested. But say you have two untitled buffers in a
pane and you close all items… You'll display prompt dialogs for both
buffers asking the user if they want to save. If the user answers yes
to the first dialog, they should see the path selection dialog before
they see the save prompt for the second buffer.
This commit uses a stack of queues to store deferred dialogs and allow
dialogs presented by the dismissal of another dialog to take precedence
over other pending dialogs.
Buffer keeps state about the value with which it fired the last
modified-status-changed event so that it doesn't fire it twice with the
same boolean value. Every piece of code that triggers the event also
needs to set this state, so now everything goes through the
`triggerModifiedStatusChanged` method.
This event now fires whenever the content of the buffer changes (after
a rate-limiting delay) with a single boolean indicating the modified
status of the buffer. There's now a separate event called
'modified-status-changed' to indicate events that change the boolean
value of the isModified method, so we don't need to fire
'contents-modified' when the underlying file is deleted for instance.
Previously, removing the last pane item also ruined our ability to
determine if the pane had focus. Now, if we're removing the last item,
we instead just go ahead and remove the entire pane. Remove contains
logic to switch focus to the next pane if its active view is focused,
which works as intended if we leave the active view in place.
Panes now trigger an event every time their active item changes,
regardless of whether the pane itself is active. Panes also trigger
events when the become active and when they are removed. The rootView
now scopes its active-item-changed event listener only to active panes,
and also listens to listens to pane activation and removal events to
update the title when switching active panes and removing the last
pane.
