Add a stack-based Boolean Operation layer node

[adamgerhant]

Closes #1816

Adds a layer Boolean operation node which performs the Boolean operation on an entire stack of vector data. This means the layer panel can now be used to adjust the operation order.

chrome_D7jptsQ7ZW.mp4

Since operations can now be performed on more than 2 shapes, the order and merging of these operations into a single vector will have to be carefully considered.

• Union: Accumulate all shapes into a single result by repeatedly setting the result to the union of of each layer and the result.
• Subtract front: Union all shapes other than the first shape, then subtract the first shape from this union.
• Subtract back: Rotate the list of vector data right one so that the last shape is at the start of the list, and subtract front.
• Intersect (area where all shapes overlap): Accumulate all shapes into a single result by repeatedly setting the result to the intersection of each layer and the result.
• Difference (area where no shapes overlap): Accumulate all shapes into a single result by repeatedly finding intersection of each layer and the result, then union this intersection with the result. This provides the area where there is at least one intersection. Then find the union of all shapes, and subtract the result.
• Divide (Show all lines for each shape): Not currently implemented due to limitations with current rendering method.

Another consideration is that a GraphicGroup can contain elements other than vector data. Currently, each element can be either another GraphicGroup, VectorData, Image, or Artboard. For GraphicGroup's and Artboards, a recursive Boolean union is applied to convert them into a a single vector. Image's are treated as default rectangles based on their height, width, and position, although this will have to be reworked. Maybe a mask should be used instead of the Boolean operation?

It would also be helpful to allow the user to specify a minimum and maximum number of overlaps for the resulting shape. For example a union would have a minimum of 0 overlaps and no maximum, intersect sets the minimum to the number of shapes - 1 and no maximum, and difference sets the minimum to 0 and maximum to 1. The UI for this could be a single slider bar with the number of ticks equal to the number of shapes in the stack, and 2 selectors for the minimum and maximum. This could be a new node "Intersect".

A more flexible implementation for the Boolean operation could take the following inputs: List of vector data (GraphicGroup), minimum overlap(RelativeOffset), maximum overlap (RelativeOffset), subtract index (Option<RelativeOffset>). The relative offset will be an enum with 2 varients, FromStart(usize) and FromBack(usize). This is necessary to ensure indices can be based of either the start of end of the vector data, so that adding a new item to the stack does not require the indices to be manually updated. For example, union will store a minimum offset of RelativeOffset::FromStart(0) and a maximum offset of RelativeOffset::FromEnd(0).

Since subtracting is fundamentally different than the intersection selection, it should be a separate node. If the subtract index is Some, then it will get that index from the list of vector data and subtract it from the Union of all vector data. This Union will be created by output of the new Intersect node.

Implementation sketch: