Simplify commenting in merge requests
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To make [reviews a first class workflow](https://gitlab.com/gitlab-org/create-stage/-/issues/13206/ "Code Review UX Roadmap") we need to simplify the way users can leave in a merge requests. Currently we present the user with too much choice.
By making the proposed changes we aiming to _increase the effectiveness of how feedback is provided in reviews_.
### Action 1: Use "Add to review" and "Comment" as button labels
- `Add to review` adds a comment to a review
- Comments of a review are unresolved threads by default.
- If the user selects "Comment only" when submitting the review https://gitlab.com/gitlab-org/gitlab/-/issues/474794, then the comments do not require to be resolved.
- `Comment` adds comment immediately
This means we will replace the following:
- "Start a review" with `Add to review`
- "Start a review" is already unclear for some people ([evidence](https://gitlab.com/gitlab-org/gitlab/-/issues/358605#supporting-evidence)). Removing it as an option then takes the state of the button from 2 to 1 with "Add to review". By moving the pending review from the footer to the top right of the page https://gitlab.com/gitlab-org/gitlab/-/issues/474794, we are adopting a pattern that is similar to e-commerce where the action "Add to cart" adds to the cart or basket.
- "Add comment now" with `Comment`
- We already use the label "Comment" on the Overview tab so in the spirit of ["use concise language" for button labels](https://design.gitlab.com/components/button#labels), I think this simplification will be fine.
### Action 2: Replies are not the time where the default action is to contribute to your own review
When replying to a comment, the primary action will be "Comment" and the secondary is "Add to review".
| Reply | Reply and new comment |
| ------ | ------ |
|  |  |
<details><summary>Current reply buttons</summary>

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This might appear like a wrong move because we are not being consistent with the placement of our buttons especially if we want to make reviews a first-class workflow. However we know that this interaction of making replies start a review instead of commenting is a pattern that causes issues for our users https://gitlab.com/gitlab-org/gitlab/-/issues/387369 https://gitlab.com/gitlab-org/gitlab/-/issues/388913 Here the context that the user is trying to reply should take precedence over the consistency of presenting the buttons in the same order.
issue