Support connected handles with multiple colors

[RunDevelopment]

This PR adds support for connected handles with multiple colors.

The styling is done is an overly complex way, but it was the only good solution I found. I'm using the same conic gradient we use for non-connected handles, and an SVG background image is used to create the hole in the middle.

Why an SVG background image? Because nothing else worked as well.

• I first tried to just use border color, but this looked horrible. The colors were rotated compared to non-connected handles, 3 colors looked horrible, and >=5 colors weren't supported at all.
• I tried using a radial gradient on top of the conic gradient to make the hole. This worked, but didn't have antialiasing. It looked horribly jagged when zoomed out.

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Other changes:

• Cache as much as possible in getTypeAccentColors.
• Fixed a bug with collapsed handles that made them white when the handle had multiple colors.
• Fixed a bug with connected input handles that caused them to use the colors of their definition type when the color of the incoming edge was the default color.