Revise semantics of proxiable_ptr_constraints

[mingxwa]

Changes

• Updated the requirements of constraint_level::trivial in proxiable_ptr_constraints from std::is_trivially_copy_constructible_v<T> into std::is_trivially_copy_constructible_v<T> && std::is_trivially_destructible_v<T> to align with the definition of std::is_trivially_copyable.
• In class template proxy<F>, removed proxy::proxy(const proxy&) = delete, proxy::proxy(proxy&&) = delete, proxy& proxy::operator=(const proxy&) = delete, proxy& proxy::operator=(proxy&&) = delete and proxy::~proxy() = delete since they are no longer needed.
• In class template proxy<F>, when F::constraints::copyability == constraint_level::trivial, proxy(proxy&&) and proxy& operator=(proxy&&) are no longer defined, so that move constructions and move assignments can fall back to trivial implementations of proxy(const proxy&) noexcept = default and proxy& operator=(const proxy&) noexcept = default.
• In class template proxy<F>, merged proxy& operator=(const proxy&) and proxy& operator=(const proxy&) noexcept; merged proxy& operator=(P&& ptr) and proxy& operator=(P&& ptr) noexcept.
• Moved friend function swap from proxy<F> into global namespace pro and removed the requires clause.
• Explicitly declared return types of function template access_proxy.
• Updated sample code for resource dictionary.
• Updated unit tests accordingly.