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/extension_host/src/wasm_host/wit.rs

@@ -999,7 +999,7 @@ impl Extension {
     ) -> Result<Result<DebugRequest, String>> {
         match self {
             Extension::V0_6_0(ext) => {
-                let build_config_template = resolved_build_task.into();
+                let build_config_template = resolved_build_task.try_into()?;
                 let dap_request = ext
                     .call_run_dap_locator(store, &locator_name, &build_config_template)
                     .await?

crates/extension_host/src/wasm_host/wit/since_v0_6_0.rs

@@ -299,15 +299,17 @@ impl From<extension::DebugScenario> for DebugScenario {
     }
 }
 
-impl From<SpawnInTerminal> for ResolvedTask {
-    fn from(value: SpawnInTerminal) -> Self {
-        Self {
+impl TryFrom<SpawnInTerminal> for ResolvedTask {
+    type Error = anyhow::Error;
+
+    fn try_from(value: SpawnInTerminal) -> Result<Self, Self::Error> {
+        Ok(Self {
             label: value.label,
-            command: value.command,
+            command: value.command.context("missing command")?,
             args: value.args,
             env: value.env.into_iter().collect(),
             cwd: value.cwd.map(|s| s.to_string_lossy().into_owned()),
-        }
+        })
     }
 }