bug(rich-text) no way to advance above a code block that is the first element

[yellis]

Describe the bug
This bug is the opposite of #41. In rich text mode, if the first element in a post is a source fence, there's no way to insert a blank line before it, anything you type gets inserted inside the fence. (The proposed Shift + Enter workaround escapes the fence downward but not upward.)

To Reproduce

1. RT mode, write some text, make it into a code block
2. Attempt to advance to before the code block. Fail at doing so.

Expected behavior
There is some way to advance the cursor to be before the code block, so as to add text or some other block element. The only way to do it now is in MD mode.

Screenshots

Desktop (please complete the following information):
Windows 11 Chrome 103

Additional context
https://meta.stackexchange.com/a/380418/51