Fix Markdown code block formatting inconsistencies.
Review Request #2157 — Created May 26, 2021 and updated
There were a few long-term inconsistencies between edit mode and render mode for Markdown code blocks: 1. Whitespace in a `code literal` wasn't preserved in render mode, even if present in edit mode. 2. The start and end of a fenced code block in edit mode was getting the background color of a `code literal`, which looked broken. 3. Some colors were different for code inside a code block between rendered mode and edit mode. This change fixes these three issues, making code look a lot more consistent between the two modes. Testing Done: Tested a handful of code blocks and inline code, making sure presentation was mostly consistent where possible. Reviewed at https://reviews.reviewboard.org/r/11616/