[Content]: Twig comparison operators

[AugustMiller]

Straight Up Craft has a couple great articles on handling values in Twig:

• Test­ing if some­thing exists: is defined, length, is not null, is not empty
• How to check if a vari­able or val­ue exists using Twig

We should provide this same information, but updated for Craft 4.x and Twig 3.x.