Experiments for the next C++ support.

• GoogleTest
  • used at Qualified
  • test name must be identifiers
  • built-in mocking
  • supports custom reporter
• Catch2
  • simple / light weight
  • test name is a string
  • tests can be split into sections
  • supports custom reporter (not implemented yet)
• bandit
  • "human-friendly" / BDD style
  • not as popular
  • uses snowhouse assertion library which is used in Igloo
  • no custom reporting
• Igloo
  • abandoned and we've been maintaining a fork
  • BDD style
• Criterion
  • C++20 requires Criterion 2.4+ which includes breaking changes affecting us