Fix `Workspace` references being leaked (#17497)

We noticed that the `Workspace` was never released (along with the
`Project` and everything that comes along with that) when closing a
window.

After playing around with the LeakDetector and debugging with
`cx.on_release()` callbacks, we found two culprits: the inline assistant
and the outline panel.

Both held strong references to `View<Workspace>` after PR #16589 and PR
#16845.

This PR changes both references to `WeakView<Workspace>` which fixes the
leak but keeps the behaviour the same.

Release Notes:

- N/A

Co-authored-by: Bennet <bennet@zed.dev>