Wrap single lines of code; horizontally scroll multi-line code blocks

## What does this MR do?
Original problem: code blocks were wrapping in issue body

* Multi-line code blocks (```) should scroll horizontally
* Single lines of code (`) should wrap

## Why was this MR needed?
Inconsistent scrolling vs wrapping behavior

## What are the relevant issue numbers?
Closes #19619 

## Screenshots (if relevant)
![Screen_Shot_2016-08-04_at_2.32.30_PM](/uploads/a4abcc81b57ffaa8dc8ce2b70a24bc21/Screen_Shot_2016-08-04_at_2.32.30_PM.png)


See merge request !5675