(feat) Increased detail in handled event breadcrumb

[robinmacharg]

Goal

Add additional metadata to handled error breadcrumbs.

Design

Simply add two additional fields to the preexisting breadcrumb metadata .

Changeset

BugsnagClient. Some small additional formatting/renaming changes were incorporated.

Tests

Unit test added.

Review

Outstanding Questions

• This pull request is ready for:
  • Initial review of the intended approach, not yet feature complete
  • Structural review of the classes, functions, and properties modified
  • Final review

• The correct target branch has been selected (master for fixes, next for
  features)
• Consistency across platforms for structures or concepts added or modified
• Consistency between the changeset and the goal stated above
• Internal consistency with the rest of the library - is there any overlap between existing interfaces and any which have been added?
• Usage friction - is the proposed change in usage cumbersome or complicated?
• Performance and complexity - are there any cases of unexpected O(n^3) when iterating, recursing, flat mapping, etc?
• Concurrency concerns - if components are accessed asynchronously, what issues will arise
• Thoroughness of added tests and any missing edge cases
• Idiomatic use of the language

[tomlongridge]

Two very minor comments