Gutenberg: Inserter malfunctions on mobile

[moorscode]

Issue Overview

When opening the inserter on screens smaller than 782pixels it works in mysterious ways.

When pressing the button (+) in the top bar, the inserter is displayed on top of the bar.
Making it unusable because scrolling up is not available.

When pressing the (+) button in the blocks content, the modal is placed off-screen on the left. The buttons on the bottom are placed below the window, having to scroll to reach them.

Steps to Reproduce (for bugs)

1. Make the screen smaller than 782 pixels wide
2. Open the inserter on any location
   

[karmatosed]

This doesn't make it any less of an issue, but there are a lot of issues with the mobile experience - it's not there yet. I am going to label this for mobile, but there needs to be a general focus and fix for all of the mobile experience, this is just one part of that.

[aduth]

The first of the two issues described here is fixed as of #1204

[mtias]

Closing as the main issue is fixed. There's ongoing work in further improving the inserter design.