Take a `shared_ptr<widget>&` parameter to express that a function might reseat the shared pointer

Reason

This makes the function's reseating explicit.

Note

"reseat" means "making a reference or a smart pointer refer to a different object."

Example, good

void ChangeWidget(std::shared_ptr<widget>& w)
{
    // This will change the callers widget
    w = std::make_shared<widget>(widget{});
}

Enforcement

• (Simple) Warn if a function takes a Shared_pointer<T> parameter by lvalue reference and does not either assign to it or call reset() on it on at least one code path. Suggest taking a T* or T& instead.
• (Simple) ((Foundation)) Warn if a function takes a Shared_pointer<T> by value or by reference to const and does not copy or move it to another Shared_pointer on at least one code path. Suggest taking a T* or T& instead.
• (Simple) ((Foundation)) Warn if a function takes a Shared_pointer<T> by rvalue reference. Suggesting taking it by value instead.