Rich Text: Caret should be positioned outside inline boundary on code pattern

[aduth]

Steps to Reproduce:

1. Navigate to Posts > Add New
2. Insert a new paragraph block
3. Type: `hello`

Expected Result:

Upon entering the terminating ` tick, it should be inferred that the formatted region is completed and that I can continue typing text as unformatted.

Actual Result:

The caret stays placed within the code region. Continued typing will be formatted as code, requiring the user to ArrowRight to escape the formatted region.

[designsimply]

Tested and confirmed that the caret lands inside the inline boundary when typing a terminating backtick.

^{Tested with WordPress 4.9.8 and Gutenberg 4.6.1 master @ 46f789a5c using Firefox 63.0.3 on macOS 10.13.6.}

[ellatrix]

Duplicate of #11276.