Text block: Failures when using shift+enter for adding line breaks

[westonruter]

TinyMCE in WordPress presently requires that you use shift+enter to add a single line as opposed to adding a paragraph. Having this engrained into my muscle memory (though I realize a simple enter creates a single line break now, I was trying the same in the Text block only to encounter a couple issues:

1. When typing First<shift+enter>second<shift+enter>third there are three lines appearing in the block as expected, but the up arrow only allows me to to go up to the second line; it does not allow be to go up to the first line.

2. When switching to the Text tab, every line other than the first is lost:

<!-- wp:core/text -->
<p>First</p>
<!-- /wp:core/text -->

[youknowriad]

The current text block is meant to contain only a single p. We probably should catch shift+enter and avoid creating new ps

Edit: An alternative would be to break out of the block and create another text block if we click shift+enter