Cleanup: enable modernize-use-equals-default check

This removes a lot of unnecessary code that is generated by
the compiler automatically.

In very few cases, a defaulted destructor in a .cc file is
still necessary, because of forward declarations in the header.

I removed some defaulted virtual destructors, because they are not
necessary, when the parent class has a virtual destructor already.

Defaulted constructors are only necessary when there is another
constructor, but the class should still be default constructible.

Differential Revision: https://developer.blender.org/D10911

.clang-tidy

@@ -35,7 +35,6 @@ Checks:  >
   -modernize-use-auto,
   -modernize-use-trailing-return-type,
   -modernize-avoid-c-arrays,
-  -modernize-use-equals-default,
   -modernize-use-nodiscard,
   -modernize-loop-convert,
   -modernize-pass-by-value,