Try solid block movers

[kjellr]

Closes #16580.

This PR implements the idea shared by @richtabor in #16580: it gives the block movers a solid color background, and hangs them off the side of the thick left block border.

I'm not totally sure about this yet — it makes the mover controls really prominent, and I'm not sure that's right. I think it could still use some iteration.

Hover:

Select:

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Still todo:

• Build in a more prominent focus state.
• Come out with a better plan for how these work with breadcrumbs. Things look a little disjointed for standard blocks, and even worse for wide/full-aligned blocks.
• Double check to make sure the changed $block-side-ui-width variable didn't have any unintended effects. It appears to be used in many places.

[enriquesanchez]

While I agree this makes the mover controls more prominent, I do feel this is an improvement over what we currently have.

Perhaps we can have the hover style only on the individual icons instead of the whole movers area?

[shaunandrews]

The spacing around the label and the drag container is a little strange for the hover state.

[karmatosed]

I personally feel this makes it a little too heavy as far as the interface goes. I think it's circling around a valid problem of visibility, just not very sure that approach is one balances it out.

[mapk]

Thanks for creating the PR, @kjellr. While I really like the connection of the mover controls to the block, and the way they are combined into one unit (not separate buttons), the heavier weight of these don't work as well in light of smaller blocks. Here's some examples that convey this:

Separator block

Paragraph block

I don't mind taking a break from this PR for now until the recent icon issues that have surfaced get resolved.

[kjellr]

I don't mind taking a break from this PR for now until the recent icon issues that have surfaced get resolved.

Yeah, I think I'm actually going to close this for now. It doesn't seem like a viable solution in its current state. We can continue iterating on the design in #16580.

Thanks, folks!