debugger: Fix the JavaScript debug terminal scenario (#33924)

There were a couple of things preventing this from working:

- our hack to stop the node REPL from appearing broke in recent versions
of the JS DAP that started passing `--experimental-network-inspection`
by default
- we had lost the ability to create a debug terminal without specifying
a program

This PR fixes those issues. We also fixed environment variables from the
**runInTerminal** request not getting passed to the spawned program.

Release Notes:

- Debugger: Fix RunInTerminal not working for JavaScript debugger.

---------

Co-authored-by: Cole Miller <cole@zed.dev>

crates/task/src/task.rs

@@ -46,7 +46,7 @@ pub struct SpawnInTerminal {
     /// Human readable name of the terminal tab.
     pub label: String,
     /// Executable command to spawn.
-    pub command: String,
+    pub command: Option<String>,
     /// Arguments to the command, potentially unsubstituted,
     /// to let the shell that spawns the command to do the substitution, if needed.
     pub args: Vec<String>,