debugger: Fix issues with restarting sessions (#33932)

Restarting sessions was broken in #33273 when we moved away from calling
`kill` in the shutdown sequence. This PR re-adds that `kill` call so
that old debug adapter processes will be cleaned up when sessions are
restarted within Zed. This doesn't re-introduce the issue that motivated
the original changes to the shutdown sequence, because we still send
Disconnect/Terminate to debug adapters when quitting Zed without killing
the process directly.

We also now remove manually-restarted sessions eagerly from the session
list.

Closes #33916 

Release Notes:

- debugger: Fixed not being able to restart sessions for Debugpy and
other adapters that communicate over TCP.
- debugger: Fixed debug adapter processes not being cleaned up.

---------

Co-authored-by: Remco Smits <djsmits12@gmail.com>

crates/dap/src/client.rs

@@ -2,7 +2,7 @@ use crate::{
     adapters::DebugAdapterBinary,
     transport::{IoKind, LogKind, TransportDelegate},
 };
-use anyhow::Result;
+use anyhow::{Context as _, Result};
 use dap_types::{
     messages::{Message, Response},
     requests::Request,
@@ -108,7 +108,11 @@ impl DebugAdapterClient {
             arguments: Some(serialized_arguments),
         };
         self.transport_delegate
-            .add_pending_request(sequence_id, callback_tx);
+            .pending_requests
+            .lock()
+            .as_mut()
+            .context("client is closed")?
+            .insert(sequence_id, callback_tx);
 
         log::debug!(
             "Client {} send `{}` request with sequence_id: {}",