[clang-tidy] added cppcoreguidelines-explicit-virtual-functions

Addresses the bugzilla bug #30397. (https://bugs.llvm.org/show_bug.cgi?id=30397)
modernize-use-override suggests that destructors require the override specifier
and the CPP core guidelines do not recommend this.

Patch by lewmpk.

Differential Revision: https://reviews.llvm.org/D58731

llvm-svn: 355093