Do not attempt to kill the process if it has already exited (#22424)

Closes #22420

This bugs seems to have existed every since `rawProcessApi.ts` was
created. `proc.killed` can be `false` even after process has exited.

src/client/common/process/rawProcessApis.ts

@@ -75,10 +75,21 @@ export function shellExec(
                 resolve({ stderr: stderr && stderr.length > 0 ? stderr : undefined, stdout });
             }
         };
+        let procExited = false;
         const proc = exec(command, shellOptions, callback); // NOSONAR
+        proc.once('close', () => {
+            procExited = true;
+        });
+        proc.once('exit', () => {
+            procExited = true;
+        });
+        proc.once('error', () => {
+            procExited = true;
+        });
         const disposable: IDisposable = {
             dispose: () => {
-                if (!proc.killed) {
+                // If process has not exited nor killed, force kill it.
+                if (!procExited && !proc.killed) {
                     if (proc.pid) {
                         killPid(proc.pid);
                     } else {
@@ -114,7 +125,8 @@ export function plainExec(
     const deferred = createDeferred<ExecutionResult<string>>();
     const disposable: IDisposable = {
         dispose: () => {
-            if (!proc.killed) {
+            // If process has not exited nor killed, force kill it.
+            if (!proc.killed && !deferred.completed) {
                 if (proc.pid) {
                     killPid(proc.pid);
                 } else {