Spacer block: Allow 1px height and improve usability in the editor

[stokesman]

In order to fix #18906, this PR changes the minimum height of the spacer block to 1px and introduces a minimum height of 48px 20px in the editor to ensure ease of block selection.

EDIT: Reduced the minimum height to 20 pixels in the editor in accordance with the current minimum height and removed some margin that was a solution for inserter overlap that is tangential to this PR.

How has this been tested?

Wordpress v5.5.1 with Gutenberg plugin v9.0.0

Types of changes

Nonbreakers

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• [n/a] My code has proper inline documentation.
• [n/a] I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR.

[talldan]

@mapk I hope you don't mind, but I added you for review as I know you were involved in the original issue.

This approach seems like it might be a reasonable trade-off. The downside that I pointed out in the issue is that the spacer size in the editor is no longer consistent with the post itself at sizes less than 20px because the block always has that minimum height in the editor.

[mapk]

The downside that I pointed out in the issue is that the spacer size in the editor is no longer consistent with the post itself at sizes less than 20px because the block always has that minimum height in the editor.

I agree here. While I understand some things just aren't going to be perfectly rendered in the Editor as they are on the front end, this particular block should. It is used to increase visual padding between elements and should reflect that padding accurately, IMO.

I really dig the exploration here, but I think we need to keep iterating.

[talldan]

Closing as superseded by #25528, thanks for the exploration on this issue. ❤️