feat: Add theme prop (#3228)

* support appearance when updating scene data

* works!

* whoops, missed a prop

* hide appearance button when prop is not set

* cleanup

* fix export + rename prop to theme

* rename to showThemeBtn, hide via react instead of css

* adapt to new state name

* add tests and css selector to target the dark mode toggle

* updated changelog and readme

* fix markdown rendering in readme

* pr feedback

src/components/DarkModeToggle.tsx

@@ -20,7 +20,8 @@ export const DarkModeToggle = (props: {
 
   return (
     <label
-      className={`ToolIcon ToolIcon_type_floating ToolIcon_size_M`}
+      className="ToolIcon ToolIcon_type_floating ToolIcon_size_M"
+      data-testid="toggle-dark-mode"
       title={title}
     >
       <input