Make tests more resilient to Skia gold failures and refactor flutter_goldens for extensive technical debt removal (#140101)

Originally landed in https://github.com/flutter/flutter/pull/139549
Originally reverted in https://github.com/flutter/flutter/pull/140085

- Remove all use of global variables.
- Always pass in all dependencies, only create them in main or in tests.
- Pass in the "print" primitive.
- Make all network traffic retry (except when run locally, when it just auto-passes).
- Enable tests to be run in random order.
- Better error messages