Put cursor in writing area when opening a document

When opening a new document or an existing one, Scratch should automatically put focus on the writing area so that the user could simply start typing.

What currently happens is that the user has to first click the editing area to focus it, and then start typing.

Steps to reproduce:
-Open a new document, using the '+' sign on the tab bar, or open an existing document, or change tabs;
-Start typing

What should happen:
Scratch should accept keyboard input and start writing to the document

What happened instead:
Nothing. The user has to click the editing area before Scratch accepts any keyboard input into the document.