Feature: Adjust Image filter

[dunkeroni]

Summary

Adds a new Canvas filter that exposes the ImageChannelOffsetInvocation and ImageChannelMultiplyInvocation functions.

• Adjust Image is now the default when opening the Filters menu, which is alphabetically pleasing and less jarring than the Canny filter.
• ImageChannel invocations now reuse the original Alpha channel (when Alpha is not the channel being modified) to preserve transparent canvas operations.
• ImageChannelOffset now lets Hue (HSV) loop over when out of [0..255] bounds

Related Issues / Discussions

Mostly satisfies #4942 but does not have contrast/sharpness abilities.

QA Instructions

A Value of 1 is no change. 0 and 2 are -255 and +255 respectively. At Value=0.5, 128 will be subtracted from each pixel in the selected channel, with results clipping to a minimum of 0.
If "Scale Values" is true, the graph will switch to using using the Multiply node, which directly uses the Value slider as the scalar input. Values above 2 can be entered manually.

adjust_image_short.mp4

Merge Plan

Ready to merge.

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• Documentation added / updated (if applicable)
• Updated What's New copy (if doing a release after this PR)

[hipsterusername]

Very cool. 🤘

[psychedelicious]

Sweet, thanks!