Tests: Add missing `@covers` tags for `WP_Block_Parser` tests.

Includes moving the data provider after the corresponding test for consistency with the rest of the test suite.

Follow-up to [43751].

Props sagardeshmukh.
See #64225.

git-svn-id: https://develop.svn.wordpress.org/trunk@62259 602fd350-edb4-49c9-b593-d223f7449a82