Add symbol support to the collection option from the association builder

[caioertai]

Purpose

This change allows the association builder to use symbols as arguments for its collection option. Which will then send them to the class implied from the reflection.

E.g.:

f.association :company, collection: :active

Which would essentially result in the same as:

f.association :company, collection: Company.active

Changes

Previously, passing a symbol to the collection key would result in an undefined method #to_a for the given symbol. This includes a check for the value being a symbol, which then sends the given symbol to the reflection klass, which, returning an object that responds to #to_a fits in easily with the current code.

Reasoning

Passing the collection argument for the association builder in the view requires a reference to the class. The proposed change allows for a more loose relation between the view and your class names, allowing for more reusability.

Known issues

• The current implementation doesn't allow for class methods with arguments. But should work nicely for simple scopes.

Notes

This is my first contribution and I have but passing knowledge of the code base. I'd appreciate an honest review and feedback and would love to dig into it more if needed. Thanks!