Remove 'IgnoreDestructors = true' from cppcoreguidelines-explicit-virtual-functions

This requirement was introduced in the C++ Core guidelines in 2016:

https://github.com/isocpp/CppCoreGuidelines/commit/1894380d0abf4d7d49a983005647e0d41ecbf214

Then clang-tidy got updated to comply with the rule.

However in 2019 this decision was reverted:

https://github.com/isocpp/CppCoreGuidelines/commit/5fdfb20b760c5307bf86873798a146fcd7e912e6

Therefore we need to apply the correct configuration to
clang-tidy again.

This also makes this cppcoreguidelines check consistent
with the other 2 alias checks: hicpp-use-override and
modernize-use-override.

Additionally, add another RUN line to the unit test,
to make sure cppcoreguidelines-explicit-virtual-functions
is tested.