Quote block: Missing styles and no difference between Default and Plain variations

[richtabor]

I've noted this is occurring with Twenty Twenty Three, as it does not include support for wp-block-styles re #44640 — but as we're pushing for block themes to not include styles or functions, we should adapt the core/quote block to look better out of the block — both the default and "Plain" styles (although we probably didn't need to include "Plain" in core…).

It's worth nothing that the core/image block's core-provided "Rounded" style is included within the block's style.scss file — ensuring it is available, regardless if the theme includes support for theme styles.

The quote block should probably do the same.

CleanShot.2023-04-12.at.14.44.54.mp4

[carolinan]

I think the block style should be removed.