Move ResolveAccParts and ResolveOmpParts from resolve-names.cpp to
resolve-directives.{h,cpp}. Move the implementation in the classes
DirectiveAttributeVisitor, AccAttributeVisitor, and
OmpAttributeVisitor to resolve-directives.cpp as well.
To allow this to happen, move EvaluateIntExpr and introduce
EvaluateInt64 to resolve-names-utils.h. The latter is also useful
elsewhere in resolve-names.cpp for converting an Expr to std::int64_t.
The other problem was that ResolveDesignator was called from the code
that was moved. At the moment it doesn't seem to be doing anything so I
removed the calls (and no tests failed). If it proves to be needed, we
can either resolve those designators in resolve-names.cpp or pass the
ResolveDesignator function in to the code that needs to call it.
Add const here as suggested?