Allow the Fill tool to flood fill raster images

[EllenGYY]

• Adds a “Raster Fill” node when the fill bucket tool is used on a raster layer. • Non-destructive: deleting the node restores the image to its original state. • Users can adjust the “tolerance” of color similarity, based on Euclidean distance in LAB color space (currently per-layer only).

Possible improvements: • Allow users to adjust and delete individual fill operations on the same layer, including their respective tolerance settings. • Add support for gradient fills.

[Keavon]

Please fix the CI failure on the test messages::tool::tool_messages::fill_tool::test_fill::ignore_raster.

[Keavon]

Checking in @EllenGYY.

[EllenGYY]

@Keavon As the semester is approaching its final weeks and I have several project / research deadlines, I’ll revisit and improve this function’s behavior after my finals on May 1st.

[Keavon]

Sounds good, thank you for the update.