Detect iPad OS 13+ with cdk/platform

#### Reproduction

Use StackBlitz to reproduce your issue: https://stackblitz.com/edit/platform-checker

Steps to reproduce:
1. Use the Platform Module
2. Try to distinguish between iOS >= 12.4.1 and iPad OS > 13


#### Expected Behavior

What behavior were you expecting to see?

I am expecting to be able to tell if the iPad is running the new iPad OS or if it is still running iOS.

#### Actual Behavior

What behavior did you actually see?

Currently there isn't a check - An iPad running the new iPad OS set's the iOS flag to false. There is no way to verify if it is running the new iPad OS

#### Environment

- Angular: 8.2.8
- CDK/Material: 8.2.1
- Browser(s): Any
- Operating System (e.g. Windows, macOS, Ubuntu): iPad OS

Start with the StackBlitz reproduction and the Angular CDK Platform Module described in the issue. Trace the existing iOS detection behavior and verify the result on iOS 12.4.1 and iPad OS 13+; done means callers can distinguish those platforms.

Written by the indexing model from the issue text.