HasManyAssociation: moved half of counter cache code to reflection

[bogdan]

There are two methods that return the counter cache column name now in code: one for belongs_to association and one for all others. That's a little confusing. So, now they are merged.

Current implementation has a lot of utility methods that accept
reflection call a lot of methods on it and exit.

E.g. has_counter_cache?(reflection)

It Breaks OOP principle XXX from the guide book and causes confusion and inability of caching even
through it always returns the same result for the same reflection object.
It can be done easier without access to the association context
by moving code into reflection itself.

e.g. reflection.has_counter_cache?

Reflection is less complex object than association so moving code there
automatically makes it simpler to understand.

[rails-bot]

r? @eileencodes

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[eileencodes]

This refactoring makes sense to me. This is a breaking change though, since you can no longer do has_counter_cache?(reflection) so there needs to be a changelog and deprecation notice for all the methods that have changed how they are used in applications.

[bogdan]

@eileencodes has_counter_cache? method was removed from HasManyAssociation that has :nodoc: flag that indicates that class is private. I don't think that undocumented classes API should be maintained in rails.

[eileencodes]

Ah yes ok - I didn't see it on the method and didn't look at the class 👍

I want to look this over a bit more before I merge but I think it's good. Thanks!