Migrate duotone block support attributes under filter instead of color

[ajlende]

Duotone filters were initially added under color support when they were only part of block supports and theme.json presets. Then, when global styles support was added, that functionality was nested under filter instead. #34667 (comment)

I lean towards styles.filters.duotone conceptually even if we were to have settings.color.palette.duotone for a palette definition it’s conceivable duotone palettes could be used for more than duotone filters either as gradient backgrounds or masks or something else

When the global styles duotone filters were added under filter, the block supports should have followed since they involve CSS filters, specifically. This will prevent some confusion that comes from the lack of consistency with that reasoning.

The duotone attribute store in style.color.duotone needs to move to style.filter.duotone.