Describe the bug
When nesting formatting, it can be difficult to select which text section we want to edit. In the following example I want to add a space on the italicized text rather than the <em>. I'm incapable of doing so, and would need to add a space after the i in is then delete text.

To Reproduce
Steps to reproduce the behavior:

1. Start a new post in the block editor.
2. Add text to a paragraph block containing "This is italicized" and add italicized formatting to the section
3. After the word "This", add more text "is a code block", then select that section and add backticks to trigger <em> formatting
4. Try to add a space to the start of "is" in the italicized section instead of the codeblock.

Expected behavior
I can add a space before is that is italicized. Right now I can only do that in the code block, or one character after the italicized section begins.

Desktop (please complete the following information):

• OS: OSX
• Browser Chrome
• Version 71.0.3578.98

Additional context

• WP 5.0.2