Fix: React Customizer controls

[tomusborne]

This fixes some Customizer bugs introduced in #600.

Using createRoot caused all of our React-based Customizer controls to break.

To fix this, I had to:

1. Convert our "wrapper" control to PHP, as createRoot doesn't build HTML in the order you would expect, which caused some of our color controls to no longer be wrapped together on one line.
2. Prevent our React controls from re-rendering on every setting change. Instead, we update state directly inside the controls.