feat(firestore): add getCountFromServer(...) method

[user08091989]

Plugin(s)

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

Current problem

There is no way now to get a count of files matching a query using your plugin, which results in huge reads being necessary. It affects the cost and performance.

Preferred solution

Add a function equivalent to getCountFromServer

Alternative options

No response

Additional context

Docs: https://firebase.google.com/docs/firestore/query-data/aggregation-queries#use_the_count_aggregation

Before submitting

• I have read and followed the feature request guidelines.
• I have attached links to possibly related issues and discussions.

[robingenz]

@ebarooni Feel free to work on this in the new year.

I suggest the following types:

export interface FirebaseFirestorePlugin {
	getCountFromServer(options: GetCountFromServerOptions): Promise<GetCountFromServerResult>;
}

export interface GetCountFromServerOptions {
	reference: string;
}

export interface GetCountFromServerResult {
	count: number;
}