feat(core): Firestore-memory and Firestore/Storage/Database-lazy entries

[jamesdaniels]

@angular/fire/firestore/memory has a variant of AngularFirestore that uses the memory-only variant of the Firestore SDK as a side-effect. This is a slimmer version of the SDK that doesn't have offline-mode, great for cutting down bundle size & speeding things up if you don't intend to enable persistence.

This would be my recommendation for use in SSR, see the sample app where I'm using the memory-only variant on the server-side and persistence enabled in the browser by reexporting AngularFirestore in sample/src/firestore.ts and replacing that file with sample/src/firestore.server.ts on the server build.

#2370

Also I've added @angular/fire/firestore-lazy, @angular/fire/firestore-lazy/memory, @angular/fire/database-lazy, and @angular/fire/storage-lazy. I will need to work on docs for these & more testing.

Small things:

• getDownloadURL pipe now does state-transfer, meaning if you use lazy you won't even have to load storage on the client side in simple cases
• PerformanceMonitoringService now uses Zone.js's start marker for increase accuracy on isStable and will track prebootComplete if you're using preboot
• ravamped fromTask more, allowing it to take in an already created/started task

[jamesdaniels]

TODO pull the little stuff into a new PR

[jamesdaniels]

Dropping most of this in favor of the minor stuff #2921