[cdac] Tighten cdac_data friend declarations

[max-charlamb]

Tightens cdac_data friend relationships to only expose internals to exact specialization.

Previously classes exposed internals to all cdac_data specializations. By changing the friend declarations to the exact specialization which needs will access the internals, we can better verify where the internals are accessed and ensure cdac_data<T> accesses the correct class.

// Example:
class Module : public ModuleBase
{
  // previous, access given to all specializations
  template<typename T> friend struct ::cdac_data
  
  // new, only cdac_data<Module> can access private class members
  friend struct ::cdac_data<Module>;
}

Note there are two special cases.

1. Some classes A are purposefully used as part of a different cdac_data<B> which may hold an instance of them. For example cdac_data<Thread> reads ThreadExceptionState offsets. In this case class A (ThreadExceptionState) declares friend to cdac_data<B> (cdac_data<Thread>).

2. Given SList is a generic implementation of a singly linked list, it seems to make sense for all cdac_data specializations to be able to access it, therefore the declaration was not changed.

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[max-charlamb]

@dotnet-policy-service agree company="Microsoft"

[lambdageek]

Thanks!

[lambdageek]

One more round of bikeshedding this comment ;-)