Setting maxHeight on overlay with flexibleConnectedTo strategy does not work, when viewport margin is also configured

#### Reproduction

Steps to reproduce:
1. Visit the [stackblitz](https://stackblitz.com/edit/understanding-overlay-03-viewport-margin-bug)
2. Click the 2 buttons


#### Expected Behavior

That the max height of 300px is respected in both cases

#### Actual Behavior

Max height is only respected, if `withViewportMargin(10)` is not configured.

#### Environment

- Angular: 8.2.13
- CDK/Material: 8.2.3
- Browser(s): `Version 78.0.3904.70 (Official Build) (64-bit)`
- Operating System (e.g. Windows, macOS, Ubuntu): `macOS Mojave`

#### Gif


#### Relevant code

```typescript
const overlayRef = this.overlay.create({
hasBackdrop: true,
positionStrategy: this.overlay.position().flexibleConnectedTo(element)

// The max height is only respected, if the viewport margin is left out
.withViewportMargin(10) // <------

.withPositions([
{
originX: 'end',
originY: 'bottom',
overlayX: 'end',
overlayY: 'top',
},
]),
width: '200px',
maxHeight: '300px',
});
```

Comienza con la reproducción vinculada de StackBlitz y el ejemplo de overlay.create que usa flexibleConnectedTo, withViewportMargin(10) y maxHeight. Traza cómo el posicionamiento conectado flexible gestiona el margen del viewport y verifica la corrección con ambos botones, asegurándote de que se respete la altura máxima de 300px en cada caso.

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