Close #24508 Main changes: As discussed in the issue 1. Change luminance calculation function to use [Relative Luminance](https://www.w3.org/WAI/GL/wiki/Relative_luminance) 2. Move the luminance related functions into color.go/color.js 3. Add tests for both the files (Not sure if test cases are too many now) Before (tests included by `UseLightTextOnBackground` are labels started with `##`): https://try.gitea.io/HesterG/testrepo/labels After: <img width="1307" alt="Screen Shot 2023-05-08 at 13 37 55" src="https://user-images.githubusercontent.com/17645053/236742562-fdfc3a4d-2fab-466b-9613-96f2bf96b4bc.png"> <img width="1289" alt="Screen Shot 2023-05-08 at 13 38 06" src="https://user-images.githubusercontent.com/17645053/236742570-022db68e-cec0-43bb-888a-fc54f5332cc3.png"> <img width="1299" alt="Screen Shot 2023-05-08 at 13 38 20" src="https://user-images.githubusercontent.com/17645053/236742572-9af1de45-fb7f-460b-828d-ba25fae20f51.png"> --------- Co-authored-by: silverwind <me@silverwind.io> Co-authored-by: Giteabot <teabot@gitea.io>
