Why this change?
We're already displaying a category's description as the title attribute
on the category section link. We should do the same for tags as well.
This PR splits up the preference that controls the count vs dot and destination of sidebar links, which is really hard to understand, into 2 simpler checkboxes:
The new preferences/checkboxes are off by default, but there are database migrations to switch the old preference to the new ones so that existing users don't have to update their preferences to keep their preferred behavior of sidebar links when this changed is rolled out.
Internal topic: t/103529.
Currently, `Tag#topic_count` is a count of all regular topics regardless of whether the topic is in a read restricted category or not. As a result, any users can technically poll a sensitive tag to determine if a new topic is created in a category which the user has not excess to. We classify this as a minor leak in sensitive information.
The following changes are introduced in this commit:
1. Introduce `Tag#public_topic_count` which only count topics which have been tagged with a given tag in public categories.
2. Rename `Tag#topic_count` to `Tag#staff_topic_count` which counts the same way as `Tag#topic_count`. In other words, it counts all topics tagged with a given tag regardless of the category the topic is in. The rename is also done so that we indicate that this column contains sensitive information.
3. Change all previous spots which relied on `Topic#topic_count` to rely on `Tag.topic_column_count(guardian)` which will return the right "topic count" column to use based on the current scope.
4. Introduce `SiteSetting.include_secure_categories_in_tag_counts` site setting to allow site administrators to always display the tag topics count using `Tag#staff_topic_count` instead.
