Full-screen overlay container doesn't work when fullscreen element is within an overlay

#### Bug, feature request, or proposal:
I believe this might be a bug.
In this example I try to load a snackbar into a container using the `viewContainerRef` config.
https://stackblitz.com/edit/angular-material-tooltip-in-container

#### What is the expected behavior?
The snackbar should align itself to the viewContainerRef that is provided.

#### What is the current behavior?
But the `_createOverlay` function does not look at this config and always creates the overlay using the `GlobalPositionStrategy` instead of `ConnectedPositionStrategy`.

There could be another root cause, and if there is please let me know.

#### What are the steps to reproduce?
I have provided a stackblitz above.

#### What is the use-case or motivation for changing an existing behavior?
There is a hand full of times i would like to load the snackbar in a container.
One in particular is the div has been maximized to full screen (so the window is not visible).
Therefore the snackbar is not visible.

#### Which versions of Angular, Material, OS, TypeScript, browsers are affected?
latest.

Inizia con la riproduzione collegata di StackBlitz e il punto di ingresso `_createOverlay`. Traccia come viene gestita la configurazione `viewContainerRef` dello snackbar rispetto alle strategie di posizionamento globale e connessa, quindi verifica che uno snackbar sia visibile e allineato all’interno di un contenitore di overlay a schermo intero.

Scritto dal modello di indicizzazione a partire dal testo della issue.