Add UI to Global styles to allow managing border radius presets

[bgardner]

What?

With the closing of #64041 and merge of #67544, add UI to Global styles to allow modification and creation of border radius preset values. This is similar to #61986 and #72301 which adds UI for spacing presets.

Why?

This will allow users to edit the border presets using the editor.

[bgardner]

CC'ing @juanfra who is working on the PR for spacing presets.

[juanfra]

Thanks for the ping, @bgardner!

This makes perfect sense, it should be quite similar to what we’re doing with the UI for spacing presets. I plan to get back to that soon. We have a newborn at home, so it’s been a beautifully hectic couple of weeks. Thanks for the patience.