Improve custom block style presentation in the block editor

[carolinan]

What problem does this address?

Now that custom block styles shows as selectable style variations in global styles,
it feels like the presentation in the block editor is dated and could be improved.

For example, the label of the panel in the block editor is Styles, which is the same as the first tab in the settings sidebar:

While in global styles they are labeled "Style variations". I think we need to use the same name across the interface.

Also kindly note that in the styles sidebar a single variation is presented on one full row and showing the full name,
while in the block editor, the names are often truncated and difficult to read because of the short width of the button,
please see #40331

I understand that not all will agree, because it takes up a lot of space, and it might be difficult to find a middle way,
but I much prefer the preview that is in the panel, over the pop out used in the editor because the pop out only shows on hover and is flickery.

[carolinan]

Ah, and also the tooltip that shows when you hover over the button that lets you select the style seems unnecessary since the text is already visible. We could remove this duplication.

[ghost]

Ah, and also the tooltip that shows when you hover over the button that lets you select the style seems unnecessary since the text is already visible. We could remove this duplication.

We could remove this duplication... when a style name is fully readable.
When style names are truncated, the tooltip is necessary. •́ ‿ ,•̀

[carolinan]

So let's give them the space they need 😃