Improve PR Review Box UI (#22986)

This PR follows: 
* #22950

### Before

The Review Box has many problems:

* It doesn't work for small screens.
* It has an anonying animation which makes the UI laggy.
* It uses "custom dropdown menu" which is very difficult to fine tune.
* `$().toggle('visible')` is not a correct call 
* jQuery just accepts any invalid `duration` argument:
`$().toggle('anyting')`
* The button is not a button.

<details>

![image](https://user-images.githubusercontent.com/2114189/219948865-6da3f39c-6fde-4c86-9e42-da5020f3d0c3.png)

</details>

### After

These problems are fixed, and eliminate many `!important` games.

<details>

![image](https://user-images.githubusercontent.com/2114189/219952744-8862fe1a-7ef1-49e4-bf92-2d0c1f104ee4.png)

![image](https://user-images.githubusercontent.com/2114189/219952771-be169a76-45fd-47a8-8f9c-b447d064f4ca.png)

![image](https://user-images.githubusercontent.com/2114189/219952784-3f52e9b7-64ce-4ad1-9553-64c33fb83042.png)

</details>

And most dropdown icons still looks good:

<details>

![image](https://user-images.githubusercontent.com/2114189/219952942-52866a00-e0f9-4af7-8fb5-eb1a8cad1ff3.png)

![image](https://user-images.githubusercontent.com/2114189/219948909-b3bfb844-f84e-4b79-ab1f-382ec66dec31.png)

</details>

Co-authored-by: delvh <leon@kske.dev>

web_src/less/_repository.less

@@ -2864,11 +2864,6 @@
   margin-top: 10px;
 }
 
-.repo-button-row .dropdown > .dropdown.icon {
-  margin-left: .25rem !important;
-  margin-right: 0 !important;
-}
-
 .wiki .repo-button-row {
   margin-bottom: 0;
 }