Dependencies tree should appear populated when the project first appears in Solution Explorer

[drewnoakes]

Today, when a project loads, the Dependencies node appears with no children, and no ▷ icon to suggest that it's expandable:

Then, some time later (commonly several seconds) the children appear:

We should have enough information at the time the tree is first created to display it in populated form, even if only via the evaluation data.

We should display the tree immediately.

[drewnoakes]

With the dependencies tree rewrite, this now appears much faster.

The root graft provider (DependenciesTreeProvider) is initialized synchronously, yet the first snapshot of data arrives asynchronously. To guarantee that the tree is populated when it first appears, we would have to introduce a wait in the tree provider which would slow down the arrival of the rest of the tree (in theory at least). In practice, any delay should be minimal as we can populate the dependencies tree from evaluation-only data, just like CPS does the rest of the tree.

Still, with the APIs we have today it'd be a sync-over-async wait, which doesn't seem great.

One other benefit of contributing to the initial population of the tree is the lack of hierarchy change events that come with a deferred update. This could contribute positively to solution load performance.

Finally, if we populate the tree early enough (which happens sometimes with the rewrite by chance — there's a race) then any previous tree expansion state is restored on project load, which is a nice change, and makes the dependencies tree behave like the rest of Solution Explorer.