Resolves "Reviews: Resolving or unresolving discussions with “Add comment now” does not work"

⚠ CE backport here: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/22303

What does this MR do?

In the batch comments feature, when you submit the comment right away, without saving it as draft first, the resolution of discussion wasn't working properly.

This adds a check that will recognize whether BatchComments are active or not and check the checkbox properly when commenting right away.

It also adds rspec tests to cover the scenarios of resolving/unresolving both when adding comment right away as well as through draft => publish review flow.

What are the relevant issue numbers?

Closes #7921 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?