Kbd rich text node traps cursor

[b-kelly]

Reported on Meta.SE.

Describe the bug

If I want to add some fancy keyboard buttons using <kbd>X</kbd>

X

They show up perfectly in the rich formatting, but when putting your cursor behind the X will make you type inside the kbd element. There is no way to type anything on that same line. Not even forcing your your cursor to appear there by double clicking (as would work in MS Word).

Reproduction steps:

• Start in markdown mode

• Add the following text:

  <kbd>X</kbd>

• Switch to rich text mode

• Placing the cursor inside the kbd element allows you to edit it, but your cursor is trapped and cannot leave the element

[b-kelly]

Closing in favor of tracking in #64.