Remove css transitions from hover/focus/active states

Created by: quinnkeast

Problem

We've received some feedback that Sourcegraph doesn't always feel "snappy."

There's a few ways to unpack this that the team is already addressing. However, there's a quick win we can follow through on: today, we use a mix of css transitions for hover/focus/active states on different UI elements across the app. These transitions add a visual "delay" to interacting with some elements, but not others, which makes the app feel less "snappy" because it literally does take longer to "respond" to user interaction.

As well, we use these transitions inconsistently throughout the app, where one element might have a transition on hover, and an otherwise-identical element next to it may not. Here's a quick example of this, which does a good job of visualizing the perceived "snappiness" with and without the transition.

https://user-images.githubusercontent.com/6304497/145795235-b832a8ed-39ba-429c-9a43-e32f5817393a.mp4

Proposal

I propose we remove all css transitions for hover/focus/active states across the product. This will immediately solve this and make the app feel more responsive to user actions.

(If, in the future, we feel there's value in specific transitions for these states, we can then design those transitions intentionally as part of Wildcard and implement them consistently across the app.)