White channel functionality in ArtNet

[roothorick]

Detailed functionality path

Extend udpartnet driver to allow sending of white channels for RGB(C)W devices that expose them directly. It could be as simple as the byte order dropdown including things like "GRBCW" or a second checkbox "send white to channels 4/5"; if a dev/contributor is feeling ambitious, change the dropdown to a string entry that accepts arbitrary combinations of R(ed), G(reen), B(lue), C(ool White), W(arm white), and 0(send zero/don't use channel)

If HyperHDR has no conception of cool / warm white, then just let W be specified multiple times so the two colors can be used together as a combined white. For a device expecting GRBCW, the user could specify GRBW0, GRB0W, or GRBWW depending on whether they prefer the cool or warm white or both.

Justification

For my light I've been using a Philips WiZ RGBCCT LED strip reflashed with Tasmota, and the most "direct" way to connect HyperHDR to Tasmota appeared to be ArtNet. Tasmota's documentation for their ArtNet implementation is incomplete; when on an RGBCW device, it's expecting GRBCW¹, not just GRB. If I select "GRB" and set 5 channels per fixture, I get usable behavior, but with the RGB channels only, the white channels just stay off.

Footnotes

1. Or possibly GRBWC ↩