Twenty Thirteen: alignment of blocks inside a full-width or wide-width group block

[sabernhardt]

With Twenty Thirteen, the editor does not center blocks within wide-width and full-width group blocks (as they are on the front end).

With the max-width of 634px, most inner blocks are centered. (List blocks will be addressed on #51157.)

Also related: #51148 (Twenty Twenty heading block)

[sabernhardt]

heading and paragraph blocks inside full-width group block (WP5.5.1)

[SergeyBiryukov]

In 49508:

Twenty Thirteen: Correct alignment of blocks inside a full-width or wide-width group block.

Props sabernhardt.
Fixes #51440.