Use most specific error name

[waltjones]

Grouping works best when the SDK sends the most specific error name available. Usually that's error.name, however there are known cases where error.constructor.name is more specific. (DOMException, for example)

This PR follows these rules:

• Prefers any value over an empty string
• Prefers any value over 'Error' where possible
• Prefers name over constructor.name when both are more specific than 'Error'