Set enableCors debug feature when emulating CF3 functions. (#4528)

Accompanies firebase/firebase-functions#1099.

With this change, users using the supported version of the Firebase Functions SDK will be able to bypass existing/default cors settings to call the emulated HTTP/callable v2 functions.

src/emulator/functionsEmulator.ts

@@ -1083,7 +1083,10 @@ export class FunctionsEmulator implements EmulatorInstance {
     envs.FUNCTIONS_EMULATOR = "true";
     envs.TZ = "UTC"; // Fixes https://github.com/firebase/firebase-tools/issues/2253
     envs.FIREBASE_DEBUG_MODE = "true";
-    envs.FIREBASE_DEBUG_FEATURES = JSON.stringify({ skipTokenVerification: true });
+    envs.FIREBASE_DEBUG_FEATURES = JSON.stringify({
+      skipTokenVerification: true,
+      enableCors: true,
+    });
     // TODO(danielylee): Support timeouts. Temporarily dropping the feature until we finish refactoring.
 
     // Make firebase-admin point at the Firestore emulator