Add User-Configurable Duotone option to Customizer

[pbking]

So that a user can control the Global Duotone options they should be presented with an option to enable/disable the duotone usage on all of the images.

• Enabling it applies the primary/background colors to the duotone attribute of all relevant blocks.
• Disabling it removes all colors from the duotone attribute of all relevant blocks.
• When a user changes Primary/Background colors using the customizer (and the option is enabled) those Primary/Background colors should be applied to all relevant blocks' duotone attributes. (Note: If we are able to accomplish this issue then this item can be simplified by just using the --primary and --background CSS variables.)
• Determining if the control is enabled or disabled should be done comparing values in the User Theme JSON rather than via theme_mod values.

The "FSE" equivalent will be to manually set the duotone values of the blocks in question in the FSE Global Styles panel.

[pbking]

This will MOST LIKELY be accomplished by adjusting the User Theme JSON block styles of all of the image blocks to have the same values of color.duotone as primary and background.

[MaggieCabrera]

I'm totally onboard with Global Styles booleans, wish we could have them! This looks like a good approach to me

[MaggieCabrera]

This one isn't actually closed