adding comment to "diff view" should have option to create discussion in the parent MR

When adding a comment to an MR, the button at the bottom "add comment" has a dropdown side-button with the option to create a discussion.

Discussions, as separate threads, can be "resolved"

When using the comment bubble on distinct lines of the diff view for an MR, the "add comment" button does not have the dropdown.

add dropdown side-button to the "add comment" button in the diff view of an MR
automatically add a link from the new discussion to the specific line in the diff view

allows "resolution" of code review comments in their original context

Extremely useful for "in context" code review.