Display block controls after typing and moving the pointer

[mtias]

From @jasmussen:

All block boundaries & controls fade out as soon as you start typing, so you can focus on the content. But as soon as you move the mouse, the boundaries & controls fade in again, as this indicates you might want to manipulate the blocks.

[ellatrix]

Done in #556.

[jasmussen]

Reopening this, as we're 90% there with #556, but not quite.

What works now is:

• click block to show boundaries
• arrow key around without boundaries disappearing
• can even use shift and other keyboard shortcuts without boundaries disappearing
• as soon as you start typing, boundaries fade out — good
• as soon as you select text, even with shift + arrow keys, boundaries fade back in — good

The missing piece is showing the boundaries of the selected block on mouse movement.

Here's a GIF:

☝️ essentially that click to show boundaries again should be unnecessary, as you have already selected the block.

[ellatrix]

Ah, apologies, I always forget about the mousemove part.