Implement IDynamicLinksService.getDynamicLink() for compatibility with react native firebase email link auth

[derMart]

Currently the implementation of getInitialLink just returns null to the client which breaks the authentication method of react native firebase using an email link only.
In their documentation there is no example code for this, but some apps implement authentication like this:
https://stackoverflow.com/questions/61564203/how-to-setup-sendsigninlinktoemail-from-firebase-in-react-native relying on the payload data of the dynamic links service.

This pull request implements

GmsCore/play-services-core/src/main/java/org/microg/gms/firebase/dynamiclinks/DynamicLinksServiceImpl.java

Lines 41 to 43 in 9e2337a

	public void getInitialLink(IDynamicLinksCallbacks callback, String link) throws RemoteException {
	callback.onStatusDynamicLinkData(Status.SUCCESS, null);
	}

by parsing the link and returning the correct payload to the client. There are a few security related checks if the package name of the link does not match the receiving package name or if it is missing. I was able to get some logins to work. It might also fix #1547 as this is related to the dynamic links service, but I haven't tested apps reported there.

best :-)