Standardise how we use SVGs

[mattseddon]

From #1078, #1073 & #1081 we now have 3 different ways of getting SVG inline into our webviews. They are:

1. Use @svgr/cli to create a React components from webview/icons and check it into source control (Icon component #1081)
2. Use @svgr along with webpack to load svgs in when bundling (Add copy button #1073)
3. Use background-image: url in scss and have webpack bundle svg (Update queued experiment icons #1078)

We should standardise and use a single approach for all of the places where we use SVGs.

My preference would be 1. I personally have no idea how to convert 3 to either 1 or 2 though.

[mattseddon]

I believe we only have two different ways of doing this now. 1 & 3.