Display railtie class name in rails initializers

[ta1kt0me]

Summary

I add a class name to recognize same macro name like load_config_initializers and load_environment_config etc in rails initializers.

[rails-bot]

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[schneems]

Not comfortable relying on an instance_variable_get(:@context) in this case. Is there no public interface for this info? Could we add one?

[ta1kt0me]

@schneems Thanks. I've updated with your advise.

[schneems]

Looks better, can you add a test, then I think we're looking good to move forwards.

[ta1kt0me]

I've changed implementation. Old one expected that @context is always Rails::Railtie's subclass. I thought it's no problem because initializer method bases Rails::Railtie. But it wasn't modulability. I only want to know a class which defineds initializer in this PR, then I've defined new interface. Please tell me if we need rebase it.

[ta1kt0me]

@schneems Anything else I need to add to this?

[schneems]

I'm fine with this. Thanks!