Node stack filenames should be relative to app root

### Problem Statement

Currently, the Node SDK captures absolute paths for stack trace filenames.

This has a number of disadvantages:
- Change of hosting config or provider might change the paths
- Paths differ by OS/username

These differences can impact error grouping.

### Solution Brainstorm

For the Electron SDK the OS/username in paths was a major issue so we already cater for this by normalising paths to the application root.

We should do something similar for the Node SDK but this will be a breaking change since it would affect customer error grouping.