(fix)NSWorkspace-specific state change notifications now use the corr…

[robinmacharg]

Goal

MacOS was incorrectly listening to a couple of automatic breadcrumb notifications on the default notification center. This PR corrects that.

Design

Extract the notifications in question and (within protective MacOS #if guards) add them to the correct NSWorkspace notification center.

Changeset

BugsnagClient.

Tests

Manual testing only. Additional methods whitelisted in mirror tests.

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