Cannot reach some text positions in nested formatting

[gwwar]

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

[youknowriad]

duplicate of #12975 ?

[youknowriad]

Closing please reopen if you think it's a different issue.

[gwwar]

Steps here are for a paragraph block, but I imagine this is the same for any nested text formatting. Maybe add a gif or screenshot in #12975 if you think this is the same issue.

[youknowriad]

I'm fine keeping it open for now and see later.

[mcsf]

cc @iseulde, if you're already looking at some text boundary stuff

[ellatrix]

Will be fixed as part of #11322.