Rendering Image traces with bilinear interpolation

[almarklein]

This is a feature request to add support for bilinear interpolation for Image traces.

At the moment, the SVG <image> element sets a style element image-rendering: crisp-edges to produce nearest-neighbor interpolation. However, in some cases, linear interpolation is preferred, so it would be nice to support this.

My proposal is to:

• Add a new property interpolate which defaults to false (nearest neighbor), and can be set ti true (for linear interpolation).
• Based on the value of this property, set (or omit) the image-rendering style attribute here

Other suggestions for the public facing API are welcome.