[2.3] Docblocks should not be followed by a blank line
minor #12993 [2.3] Docblocks should not be followed by a blank line (GrahamCampbell)

This PR was squashed before being merged into the 2.3 branch (closes #12993).

Discussion
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[2.3] Docblocks should not be followed by a blank line

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | N/A
| License       | MIT
| Doc PR        | N/A

There should be no blank line(s) between phpdocs that document properties, interfaces, classes, functions, or traits. This pull request was a test run of a new php-cs-fixer: https://github.com/FriendsOfPHP/PHP-CS-Fixer/pull/864.

Commits
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4e7ba1b [2.3] Docblocks should not be followed by a blank line