feat: Emulator support for Firestore

[sklink]

Plugin(s)

• Analytics
• App
• App Check
• Authentication
• Crashlytics
• Cloud Firestore
• Cloud Messaging
• Cloud Storage
• Performance
• Remote Config

Current problem

Unable to connect to locally running Firestore emulator

Preferred solution

Would like to use the connectFirestoreEmulator method from firebase/firestore to connect to an emulator either at localhost or through a reverse proxy. Note that reverse proxy requires the initializeFirestore(app, { host }); method because connectFirestoreEmulator requires a port.

Alternative options

I did try to use the Firebase SDK methods to connect to the emulator but I can see the network requests still routing through the live Firestore url.

Additional context

I started writing a PR for this but an issue, as mentioned above, is that the connectFirestoreEmulator does not allow for host-only, making reverse proxy unusable. In that case, using initializeFirestore(app, { host }); instead works.

Here's the method for web.ts in capacitor-firebase/firestore, but I'm unsure whether initializeFirestore here is going to cause issues:

  export interface UseEmulatorOptions {
    host: string;
    port?: number;
  }
 
  // ... In the FirebaseFirestoreWeb definition

  public async useEmulator(options: UseEmulatorOptions): Promise<void> {
    const firestore = getFirestore();
    
    if (options.port) {
      connectFirestoreEmulator(firestore, options.host, options.port);
    } else {
      initializeFirestore(firestore.app, {
        host: options.host
      });
    }
  }

I have not looked at the native code to see what might need to be changed there.

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