[clang-tidy] documentation of cppcoreguidelines-virtual-class-destructor claims behavior that does not exist

As explained in #184184: In the documentation of `cppcoreguidelines-virtual-class-destructor`, the following claim:

> This check implements [C.35](http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#rc-dtor-virtual) from the C++ Core Guidelines.

is incorrect and should be weakened significantly.

There is an alternative proposal in #184184 , to treat the current behavior of this rule as a bug and fix the behavior, or to add a new optional mode of this rule that satisfies the claim. However, that ticket may instead be resolved by adding a new standalone check -- in which case, the documentation for this existing rule will still be wrong.

Start with the documentation for `cppcoreguidelines-virtual-class-destructor` and review the behavior and alternatives discussed in #184184. Update the claim that this check implements C.35 so it accurately reflects the existing rule, while accounting for whether #184184 adds a new check or changes this one.

Written by the indexing model from the issue text.