Turn off font family and size controls

[justintadlock]

The goal before release is to lock down most design tools in favor of using block styles.

Currently, there are no fontSize and fontFamily booleans under settings.typography via theme.json:

• theme.json needs "fontSize" and "fontFamily" properties in settings>typography to allow disabling of the controls while keeping the CSS WordPress/gutenberg#50330

There are ways around this, such as setting fontSizes and fontFamilies to an empty array for each block or to filter this on the PHP end. We need to decide on the best solution that also lets us open this up while in development mode.