Include `event.contexts.device.processor_count` for browser and node

### Problem Statement

Most platforms now have a way to get the CPU count.

### Solution Brainstorm

In browsers `navigator.hardwareConcurrency` has been around for a while. Safari apparently caps this as 2 for iOS and 8 for macOS.

Node.js has had [`os.cpus()`](https://nodejs.org/api/os.html#oscpus) since pre v1.