vm_ptr.h: Improve try_read()

[elad335]

• Allow if T is not a default constructible type, use bit cast to construct it. Fixes reading vm::ptr<vm::ptr<T, const u32>> for example.
• Simplify usage, no longer needing to manually construct the destination data and thus always spelling its type. (f.e. if (CellSaveDataSetList list{}; setList.try_read(list)) can become if (auto [ok, list] = setList.try_read(); ok)
• Use std::addressof where needed.

[elad335]

I kept old variant because of types such as atomic_t<> which are not copy constructible.