Monaco can not deal with color formats other than 6-digit hex, so we
convert the colors for it via new
[`tinycolor2`](https://github.com/bgrins/TinyColor) dependency (5kB
minzipped).
Also, with the addition of the module, we can replace the existing
`hexToRGBColor` usage, I verified it is compatible with the current
tests before removing the function.
Fixes: https://github.com/go-gitea/gitea/issues/25770
