fix(core): drain stdout before exit in print-affected (#12559)

Piping a large print-affected output to another command, such as cat or jq, resulted in broken json
output as the node process can exit before the output is fully written. The process.stdout stream
needs to wait to drain before process.exit.

packages/nx/src/command-line/affected.ts

@@ -130,6 +130,7 @@ export async function affected(
         break;
       }
     }
+    await output.drain();
   } catch (e) {
     printError(e, args.verbose);
     process.exit(1);

packages/nx/src/utils/output.ts

@@ -267,6 +267,16 @@ class CLIOutput {
 
     this.addNewline();
   }
+
+  drain(): Promise<void> {
+    return new Promise((resolve) => {
+      if (process.stdout.writableNeedDrain) {
+        process.stdout.once('drain', resolve);
+      } else {
+        resolve();
+      }
+    });
+  }
 }
 
 export const output = new CLIOutput();