angular element with overlay rendered in overlay

#### Reproduction

https://github.com/rcketscientist/AngularElementOverlayRepro

Steps to reproduce:
1. Create an Angular Element that leverages a CdkOverlay Material widget (tooltip, select, etc)
2. Place that selector in a CdkOverlay (MatDialog, for example).

As soon you interact with the "inner" CdkOverlay by hovering over the tooltip or activating the select, the host CdkOverlay will just crash without an error message I can pick up on.

This might not really be a bug, but rather a limitation of Angular Elements, but being that it can be triggered with simple widgets I wonder if there's not some way I can get the Angular Elements to play well with the host.

The Angular Elements work fine when not hosted in a CdkOverlay.


#### Expected Behavior

What behavior were you expecting to see?
CdkOverlay within Angular Element plays well with the host.

#### Actual Behavior

What behavior did you actually see?
Acitvation of the CdkOverlay within an Angular Element causes the host CdkOverlay to silently crash.

#### Environment

- Angular:8
- CDK/Material: 8
- Browser(s): Chrome
- Operating System (e.g. Windows, macOS, Ubuntu): Win/Mac

Commencez par la reproduction sur https://github.com/rcketscientist/AngularElementOverlayRepro et reproduisez l'échec avec Angular 8, CDK/Material 8 et Chrome. Étudiez l'interaction entre le widget CDK Overlay d'un Angular Element et son overlay hôte ; le travail est terminé lorsque l'interaction avec le tooltip ou le select ne fait plus silencieusement planter l'overlay hôte, ou lorsque la limitation est documentée.

Rédigé par le modèle d'indexation à partir du texte de l'issue.