Implement comment_hook_info()

Works.

Patch rerolled.

This lets you put all your comment stuff in a separate include in case comment module is disabled, but it's grouping very rare things like delete with view, so if comment module is enabled, all that code is going to be loaded again just because one is, but now with the extra overhead of an additional include etc.

I'm also not really keen in general on having hook_hook_info() implemented by every module, since it has no way at all to deal with dynamic hook names yet. Most of these hooks are or will be implemented generically by the entity system (hook_comment_load() already is), so really entity module ought to be able to dynamically handle that, but it can't, much less arbitrary things like hook_form_FORM_ID_alter().

So.. I think we should re-visit hook_hook_info() - what the patterns should be, whether we could reverse it to allow modules to explicitly register hook implementations instead (or require explicit registration which is being discussed elsewhere).

See #2233261: Deprecate hook_hook_info()

Adding relationships and not in summary.