Fix Project strong reference leaks (#22470)

Closes https://github.com/zed-industries/zed/issues/21906

* After https://github.com/zed-industries/zed/pull/21238,
`TerminalPanel` and `Project` strong references were moved into
`Pane`-related closures, creating a cycle, that did not allow
registering project release and shutting down corresponding language
servers

* After https://github.com/zed-industries/zed/pull/22329, a special
`Editor` was created with a strong reference to the `Project` which
seemed to do nothing bad in general, but when a working Zed was running
a Zed Dev build, had the same issue with preventing language servers
from shutting down.

The latter is very odd, and seems quite dangerous, as any arbitrary
`Editor` with `Project` in it may do the same, yet it seems that we did
not store them before the way git panel does.

I have tried creating a test, yet seems that we need to initialize a lot
of Zed for it which I failed — all my attempts resulted in a single
language server being present in the `Project`'s statuses.

Release Notes:

- Fixed language servers not being released between project reopens