feat(overlay): `hostClass` property that sets a class on the rendered element to allow for CSS encapsulation

[ParadoxSpiral]

Feature Description

Add a hostClass property besides the panelClass property that sets the classes on the inserted element instead of the overlay pane, e.g

<div id="cdk-overlay-0" class="panel-class" ...>
  <app-some-overlay class="host-class">...</app-some-overlay>
</div>

Use Case

This allows using proper CSS view encapsulation for the component styles, because then you could do this:

:host.host-class {
  // Some property
}