[Design] Commenting in merge requests with context
## Proposal
Introduce an ability to toggle between modes of `comment` and `review`. The modes will adapt the button order based on who the user is (author or reviewer) and the context that the note is in (reply or new note) to determine default button order and based on user action we would remember that preference for future.
[Figma](https://www.figma.com/design/0ABBYYEvZTroTREb7yydtk/Comments-and-Diffs?node-id=151-93525&t=MlrSsSW15jGDHksE-1)

This is a design concept that combines ideas from these related issues
- https://gitlab.com/gitlab-org/gitlab/-/work_items/501254+
- https://gitlab.com/gitlab-org/gitlab/-/work_items/388913+
- https://gitlab.com/gitlab-org/gitlab/-/work_items/358605+
- https://gitlab.com/gitlab-org/ux-research/-/work_items/3269+
### Assumptions
1. "Add to review" should always be the default action
- Respecting original intent of the feature
3. Who the user is can be simplified to IsReviewer (true/false)
- We can assume that in most cases an Author would not use a review as their default action and that since we don't know what role a participant is that we would default to commenting actions.
4. The context of the note can be simplified to IsReply (true/false)
- Replying to a thread was a common feedback that we should just default to "Reply" rather than adding to a review so we will start with that as default actions.
### Mockups
| Comment - Add to review | Comment - Submit review | Comment - Comment now |
| ------ | ------ | ------ |
| {width=884 height=600} | {width=884 height=600} | {width=884 height=600} |
| Reply - Add to review | Reply - Submit review | Reply - Reply comment |
| ------ | ------ | ------ |
| {width=900 height=536} | {width=900 height=540} | {width=900 height=540} |
| Overview - Add to review | Overview - Submit review | Overview - Comment |
| ------ | ------ | ------ |
| {width=900 height=384} | {width=900 height=384} | {width=900 height=384} |
## Problem background
Today when a user is ready to comment they are presented with actions in this order:
- Add to review
- Add comment now
- Cancel
{width=900 height=500}
This is was an intentional decision to order the buttons in this manner (2018)
- https://gitlab.com/gitlab-org/gitlab-foss/-/work_items/53346+
- https://gitlab.com/gitlab-org/gitlab/-/work_items/8535+
The original intent behind 'Start a review/Add to review' aimed to encourage users to leverage reviews for batch comment processing and approvals. However contextual factors such as who was taking the action (the author or a reviewer) and whether they were replying to an existing comment or creating a new note has lead to users making errors when trying to leave feedback.
The problem with this is users do not always want to add a comment to a review, for example when replying in a thread https://gitlab.com/gitlab-org/gitlab/-/issues/387369#note_2887505187:
>>>
A reply should really not start a review process. I spend replying to comments all day long and dozens of times a day I have to _edit comment_ \> _copy content_ \> _cancel_ \> _delete comment_ \> _make comment again_ \> _click on "add comment directly" with mouse_. It's super annoying.
>>>
Related history https://gitlab.com/gitlab-org/gitlab/-/issues/369485+
Or when using `cmd`+`enter` to submit their feedback, it automatically adds it in as part of a review when the user wants to send the comment immediately. This is a common theme that has been expressed by GitLab team members and the community https://gitlab.com/gitlab-org/gitlab/-/work_items/222334+.
issue