Allow prefetching of topsite with observeForever and allow to update homefragment in onCreateView

[MarcLeclair]

Allowing to do so would save us ~100-150ms (time taken on a g5+). Note: the time on higher end device can be between 20-40ms.

I used nanoscope to profile a non debugabble build on start up (simpleperf is still struggling a bit right now so I used this), the UI isn't very friendly and works better on chrome at the moment. At ~1220656473ns in the profile, we can see the LiveData.setValue() callback after our first traversal. By prefetching our topsites, we'd be able to avoid this callback and show our topsites on the first layout pass.
noprefetch.html.zip

On top of that, we have an issue where we update our UI with the TopSites and collectionStorage through the call consumeFrom which triggers a coroutine. The hiccup here is that the launch isn't triggered right away on our UI thread which means that on our first view traversal, even though our data should be available, we don't update it there which means a slower start up since we have to wait for the consumeFrom callback.

Here's an image that depics this better. The first call stack on the right is our first traversal (so the firefox logo showing, the url bar on the bottom, etc...). Topsites will then get drawn after the livedata callback which occurs where the two lines intersect ( the gray box in the bottom left indicates that this triggers our topsite change with HomeFragment$onTopSiteChange

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[stale]

See: #17373 This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.