Dynamic viewport height

#### Bug, feature request, or proposal:
Dynamically adjust the size of the table according to its content

#### What is the expected behavior?
It would be interesting to be able to define only the maxheight of the table and to adjust it dynamically according to the amount of data it contains until it reaches the maxheight. When the size is max height the virtualscrolling is available.

#### What is the current behavior?
When the cdk-virtual-scroll-viewport has no defined height it does not display all available values. If the height is defined the viewport displays all lines but when it is undefined just a few lines are displayed.

#### What are the steps to reproduce?
[Stackblitz](https://stackblitz.com/edit/angular-cdk-demo-virtual-scroll-jqpazr?embed=1&file=app/app.component.ts)

#### What is the use-case or motivation for changing an existing behavior?

#### Which versions of Angular, Material, OS, TypeScript, browsers are affected?
latest cdk-experimental

#### Is there anything else we should know?

Comienza ejecutando la reproducción vinculada en StackBlitz e inspecciona el comportamiento de cdk-virtual-scroll-viewport cuando su altura no está definida. El trabajo estará terminado cuando la tabla crezca con su contenido hasta una altura máxima configurada, mientras el desplazamiento virtual siga disponible en ese límite.

Escrito por el modelo de indexación a partir del texto del issue.