Eyedropper tool doesn't support Vello

[Keavon]

• Desktop (Desktop: Add Eyedropper tool support with native Vello #3684)
• Web (Fix the Eyedropper tool on web with Vello and on desktop with SVG #3886)

There is a related bug on web where any raster content in the document causes the current implementation to not work:

Uncaught (in promise) SecurityError: Failed to execute 'getImageData' on 'CanvasRenderingContext2D': The canvas has been tainted by cross-origin data.

Future improvement on desktop: #3800