Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Gadgets/Stdrev: Interpret C++98/03 dropdown as C++03 instead of C++98
  Gadgets/Stdrev: Split C++98 and C++03 standards
  Gadgets/Stdrev: Replace uses of mark identifiers with visibility map
  Gadgets/Stdrev: Refactor get_visibility_map to be more generic
  Gadgets/Stdrev: Add rev-works-with-fully-closed-ranges test
  Gadgets/Stdrev: Added support for C++20
  Gadgets/Stdrev: Removed FIXME
  Gadgets/Stdrev: Handle all cases of fully closed ranges

Author: PeterFeicht