navigator pane: show item count

Hey, OAW. There are almost always tradeoffs in design choices. By fixing a count to the bottom of the window, we reduce the useable window space with an element that not everyone may be interested in. It's a small thing, but those things can add up. There are some apps with way too many layers of chrome that can end up taking up as much space as the actual content. We could make it a setting, but more settings means more complexity and potential confusion.

Anyway, I'm not really advocating for the current or previous design, just noting that what you see as "demonstrably inferior" can still be seen from other perspectives. We try to balance those and come to reasonable conclusions. The current conclusion may or may not stick. I think I'd personally still prefer to show counts in the sidebar like was mentioned previously, but we'll see where we end up.

ref: dev/core/core#9298