Comment Color Brightness

[arcticicestudio]

Bound to nordtheme/nord#94

This issue will implement the increase of the comment color (nord3) brightness by 10% from a lightness level of ~35% to ~45%.

➜ Please see nordtheme/nord#94 for all details about this design change decision.

⚠️ NOTE: This will also deprecate the custom comment brightness configuration because it won't be necessary anymore for users to increase the brightness on their own.
A deprecation warning will be added to notify all users who have set a custom value for the nord-comment-brightness configuration variable.