Custom block row labels defined on `admin.components.Label` were not
rendering despite existing in the config. Instead, if a custom label
component was defined on the _top-level_ blocks field itself, it was
incorrectly replacing each blocks label _in addition_ to the field's
label. Now, custom labels defined at the field-level now only replace
the field's label as expected, and custom labels defined at the
block-level are now supported as the types suggest.
6c19579ccf