Bundled Themes: Twenty Twenty inconsistent top and bottom margins for...

Bundled Themes: Twenty Twenty inconsistent top and bottom margins for `.alignwide` and `.alignfull` on Chrome vs Safari.

Fixes the inconsistent margins for `alignwide` and `alignfull` classes used on Cover Block when it is the first block on a page.

Props kthmd, utz119, nikhilbhansi.
Fixes #49435.
Built from https://develop.svn.wordpress.org/trunk@47820


git-svn-id: https://core.svn.wordpress.org/trunk@47596 1a063a9b-81f0-0310-95a4-ce76da25c4cd