Allow adding new lines (<br>) without a keyboard in Gutenberg

[thehenrybyrd]

Expected behavior

I expected to be able to add a new line within a paragraph block.
On a laptop or with an external keyboard, this is done by pressing "shift" and "return" together.

Actual behavior

Instead, there is no way to add a new line, other than entering "HTML Mode" and using a <br>.

Tested on iPhone SE, iOS 13.1.2, WPiOS 14.3

Requested in #2859616-zen

[thehenrybyrd]

Related: #9111

[hypest]

Closing in favor of wordpress-mobile/gutenberg-mobile#559 since that's older and with more discussion. Let me know if this needs to stay open too, thanks!