Capture mouse events when rendering disconnected overlay

We do so by replacing `EventHandler::capture` with a new `::capture_all` method.
After switching to mouse regions as part of zed-industries/zed#1081, overriding
`dispatch_event` on `EventHandler` wasn't enough anymore because mouse interactions
take place on a privileged code path that runs *before* dispatching any event.

With this change, `EventHandler` will now push a mouse region that intercepts all
mouse interactions, as well as pushing a cursor region that resets the cursor style
to `Arrow`.

One interesting change as part of this is that we've removed the ability to see which
event we are capturing: we were not using this capability anyway and `capture_all` provides
a simpler interface, so I went with that. In the future, we can opt into capturing specific
events or mouse interactions if there's a code path that needs that.

Offline projects

Co-authored-by: Antonio Scandurra <me@as-cii.com>

Introduce support for C++

Co-authored-by: Antonio Scandurra <me@as-cii.com>

Co-Authored-By: Max Brunsfeld <max@zed.dev>

This makes it more evident that both languages share the same language
server.

Co-Authored-By: Max Brunsfeld <max@zed.dev>

Until the host has sent an UpdateProject message to populate the project's
metadata, there is no reason to update contacts.

* env_logger
* prost-build
* bindgen

* Make `UnregisterProject` a request. This way the client-side project can wait
  to clear out its remote id until the request has completed, so that the
  contacts panel can avoid showing duplicate private/public projects in the
  brief time after unregistering a project, before the next UpdateCollaborators
  message is received.
* Remove the `RegisterWorktree` and `UnregisterWorktree` methods and replace
  them with a single `UpdateProject` method that idempotently updates the
  Project's list of worktrees.

This prevents memory leak errors in tests, due to parked tasks waiting
for RPC responses.

Introduce a ProjectStore that lets you iterate through all open projects.
Allow projects to be made public by clicking the lock.

Report the correct app version when sending panics to server

Previously, we were just relying on the `ZED_APP_VERSION` environment
variable without consulting `Platform::app_version`. That would always
report "dev" as the app version because `ZED_APP_VERSION` is only used
for testing.

Don't reuse the same diagnostic group id across buffers

This lets us use the group id as the key for an `ElementState`, which
fixes a panic that would occur in project diagnostics when opening it
while there were multiple diagnostic groups with the same id.

Context menu polish

Jump to diagnostic

Now you simply specify a text, an action and a style and GPUI will
take of rendering it properly. This is simpler compared to always
providing a custom element and should make tooltip more consistent
across the UI.