Add fields to WP_Block_Type

As part of #47620 and the RFC for block registeration. Server registered blocks are missing some fields. These changeset includes them.

Props spacedmonkey, aduth.

Fixes #48529.


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git-svn-id: https://core.svn.wordpress.org/trunk@47649 1a063a9b-81f0-0310-95a4-ce76da25c4cd