Add UI scale

[mrleblanc101]

What problem does this feature solve?

Currently we can zoom the Devtools entirely using CMD + or CMD -.
But this will affect other parts of the Devtools, not only the Vue Devtools plugin.
It would be nice if we could have a UI Scale slider in the Settings like the Nuxt Devtools.

This shouldn't be too hard if the UI is made using rem/em instead of px.
We could simply increase the base font-size depending on the user preference.
Here are some screenshot from the Nuxt Devtools setting page: