Update the way `pane::RevealInProjectPanel` is handled to ensure that,
regardless of whether the file belongs to any open project, the project
panel is always activated and focused.

This refactor is a result of some internal feedback after changing its
handling so as to show a notification stating that the item that the
user was trying to reveal didn't belong to an open project
– https://github.com/zed-industries/zed/pull/51246 .

We feel users are probably already used to relying on `cmd-shift-e` (on
macOS), in pretty much every context, in order to open the project
panel, and so having situations where it doesn't actually happen seems
like a bad user experience.

Relates to #23967 

Release Notes:

- Improved `pane: reveal in project panel` to open the project panel,
even if working with an unsaved buffer.