[docs] Add animation performance advice

What does this MR do?

docs for animations that don't trigger layout

Are there points in the code the reviewer needs to double check?

Things I wanted to doc:

• prefer transforms
• both in CSS and in JS (e.g $.css or el.style)

Why was this MR needed?

we have some janky animations

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Review
  • Has been reviewed by Frontend
• Conform by the style guides

What are the relevant issue numbers?