Backslash pipe incorrectly escaped in inline code in markdown tables

As detailed in #322503 (comment 535015337), this is working as designed. The documentation is being updated in Document escaping pipe character in markdown ta... (!107119 - merged)

---

original description

The following markdown code

| header |
| ------ |
| `one\|two` |

should show one\\\\\\\\|two as the inline code, but instead shows this:

This problem existed before !45922 (merged) as well as after.

We need to investigate if changes in MarkdownPreEscapeFilter or MarkdownPostEscapeFilter can fix this.